When adding the same static SNAT entries to different VRFs (VRF ID  ~ nat-instances) an error is received - which is understandable. However, could you add a log or an error message explaining the cause for further troubleshooting.

curl -XPUT -H "Content-Type: application/json" -u admin:admin http://localhost:8183/restconf/config/ietf-nat:nat-config/nat-instances/nat-instance/0/mapping-table/mapping-entry/1/ -d '{ "mapping-entry" : { "index": 1, "type": "static", "internal-src-address": "192.168.120.7", "external-src-address": "192.168.37.101" } }'

curl -XPUT -H "Content-Type: application/json" -u admin:admin http://localhost:8183/restconf/config/ietf-nat:nat-config/nat-instances/nat-instance/1/mapping-table/mapping-entry/1/ -d '{ "mapping-entry" : { "index": 1, "type": "static", "internal-src-address": "192.168.120.7", "external-src-address": "192.168.37.101" } }'

will hit the following universal error:

2017-06-21 13:00:19.713 UTC [qtp1050196275-1810] WARN i.f.h.d.i.ModifiableDataTreeDelegator - Failed to apply all changes
io.fd.honeycomb.translate.write.registry.WriterRegistry$BulkUpdateException: Bulk update failed at: InstanceIdentifier{targetType=interface org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instan
ces.nat.instance.mapping.table.MappingEntry, path=[org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.NatConfig, org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.NatInstances
, org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.NatInstance, org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.nat.instance.Mapping
Table, org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.nat.instance.mapping.table.MappingEntry]} ignored updates: [KeyedInstanceIdentifier{targetType=interface org.opendaylight.yang.ge
n.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.nat.instance.mapping.table.MappingEntry, path=[org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.NatConfig, org.opendaylight.yang.gen.
v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.NatInstances, org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.NatInstance[key=NatInstanceKey [_id=1]], org.opendaylight.yan
g.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.nat.instance.MappingTable, org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.nat.rev150908.nat.config.nat.instances.nat.instance.mapping.table.M
appingEntry[key=MappingEntryKey [_index=1]]]}]
at io.fd.honeycomb.translate.impl.write.registry.FlatWriterRegistry.bulkUpdate(FlatWriterRegistry.java:227) ~[translate-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.impl.write.registry.FlatWriterRegistry.update(FlatWriterRegistry.java:111) ~[translate-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.data.impl.ModifiableDataTreeDelegator$DelegatingConfigSnapshot.processCandidate(ModifiableDataTreeDelegator.java:132) ~[data-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.data.impl.ModifiableDataTreeManager$ConfigSnapshot.commit(ModifiableDataTreeManager.java:108) [data-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.data.impl.WriteTransaction.submit(WriteTransaction.java:136) [data-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.data.impl.ReadWriteTransaction.submit(ReadWriteTransaction.java:95) [data-impl-1.17.07-SNAPSHOT.jar:na]
at org.opendaylight.netconf.sal.restconf.impl.BrokerFacade.putDataViaTransaction(BrokerFacade.java:944) [sal-rest-connector-1.4.3-Boron-SR3.jar:na]
at org.opendaylight.netconf.sal.restconf.impl.BrokerFacade.commitConfigurationDataPut(BrokerFacade.java:232) [sal-rest-connector-1.4.3-Boron-SR3.jar:na]
at org.opendaylight.netconf.sal.restconf.impl.RestconfImpl.updateConfigurationData(RestconfImpl.java:820) [sal-rest-connector-1.4.3-Boron-SR3.jar:na]
at org.opendaylight.netconf.sal.restconf.impl.StatisticsRestconfServiceWrapper.updateConfigurationData(StatisticsRestconfServiceWrapper.java:136) [sal-rest-connector-1.4.3-Boron-SR3.jar:na]
at org.opendaylight.netconf.sal.rest.impl.RestconfCompositeWrapper.updateConfigurationData(RestconfCompositeWrapper.java:86) [sal-rest-connector-1.4.3-Boron-SR3.jar:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_131]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_131]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_131]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_131]
at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.uri.rules.ResourceObjectRule.accept(ResourceObjectRule.java:100) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1542) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1473) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409) [jersey-server-1.19.1.jar:1.19.1]
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409) [jersey-servlet-1.19.1.jar:1.19.1]
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558) [jersey-servlet-1.19.1.jar:1.19.1]
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733) [jersey-servlet-1.19.1.jar:1.19.1]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [javax.servlet-api-3.1.0.jar:3.1.0]
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:845) [jetty-servlet-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1689) [jetty-servlet-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.servlets.CrossOriginFilter.handle(CrossOriginFilter.java:308) [jetty-servlets-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.servlets.CrossOriginFilter.doFilter(CrossOriginFilter.java:262) [jetty-servlets-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1668) [jetty-servlet-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:581) [jetty-servlet-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:513) [jetty-security-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1180) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511) [jetty-servlet-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1112) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:513) [jetty-security-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.handler.gzip.GzipHandler.handle(GzipHandler.java:397) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.Server.handle(Server.java:524) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]

at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:319) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:253) [jetty-server-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273) [jetty-io-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95) [jetty-io-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93) [jetty-io-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303) [jetty-util-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148) [jetty-util-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136) [jetty-util-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671) [jetty-util-9.3.11.v20160721.jar:9.3.11.v20160721]
at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589) [jetty-util-9.3.11.v20160721.jar:9.3.11.v20160721]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
Caused by: io.fd.honeycomb.translate.write.WriteFailedException: io.fd.vpp.jvpp.VppCallbackException: vppApi.snat_add_address_range_reply failed with error code: -81
at io.fd.hc2vpp.common.translate.util.JvppReplyConsumer.getReplyForWrite(JvppReplyConsumer.java:73) ~[vpp-translate-utils-1.17.07-SNAPSHOT.jar:na]
at io.fd.hc2vpp.common.translate.util.JvppReplyConsumer.getReplyForWrite(JvppReplyConsumer.java:56) ~[vpp-translate-utils-1.17.07-SNAPSHOT.jar:na]
at io.fd.hc2vpp.nat.write.MappingEntryCustomizer.writeCurrentAttributes(MappingEntryCustomizer.java:68) ~[nat2vpp-1.17.07-SNAPSHOT.jar:na]
at io.fd.hc2vpp.nat.write.MappingEntryCustomizer.writeCurrentAttributes(MappingEntryCustomizer.java:41) ~[nat2vpp-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.impl.write.GenericListWriter.writeCurrentAttributes(GenericListWriter.java:50) ~[translate-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.util.write.AbstractGenericWriter.writeCurrent(AbstractGenericWriter.java:45) ~[translate-utils-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.impl.write.GenericListWriter.writeCurrent(GenericListWriter.java:84) ~[translate-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.util.write.AbstractGenericWriter.update(AbstractGenericWriter.java:81) ~[translate-utils-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.impl.write.registry.SubtreeWriter.update(SubtreeWriter.java:69) ~[translate-impl-1.17.07-SNAPSHOT.jar:na]
at io.fd.honeycomb.translate.impl.write.registry.FlatWriterRegistry.bulkUpdate(FlatWriterRegistry.java:211) ~[translate-impl-1.17.07-SNAPSHOT.jar:na]
... 59 common frames omitted
Caused by: io.fd.vpp.jvpp.VppCallbackException: vppApi.snat_add_address_range_reply failed with error code: -81
2017-06-21 13:00:19.713 UTC [qtp1050196275-1810] INFO i.f.h.d.i.ModifiableDataTreeDelegator - Trying to revert successful changes for current transaction