File does not exist when trying to call a POST.

This is the data I'm sending to my publish service:

{"Persoon":"5","TransactieType_ID":1,"DatumEnTijd":"2012-04-23T18:25:43.5110000Z","Bedrag":0.15,
}

My microflow

The mapping:

I have set "Enable Create" to true, thus expecting a new object being created. I however recieve this error:
 

com.mendix.core.CoreRuntimeException: Exception occurred in action '{}', all database changes executed by this action were rolled back
	at com.mendix.core.actionmanagement.CoreAction.processErrorState(CoreAction.java:303)

Caused by: com.mendix.core.CoreException: com.mendix.modules.microflowengine.MicroflowException: LocalFileSystemStore:: File does not exist for key: 11
	at Lunch.POST_DataTest (Import with mapping : 'Import from JSON')
	at {}

Advanced stacktrace:
	at com.mendix.core.component.InternalCore.execute(InternalCore.java:389)

Caused by: com.mendix.modules.microflowengine.MicroflowException: LocalFileSystemStore:: File does not exist for key: 11
	at Lunch.POST_DataTest (Import with mapping : 'Import from JSON')
	at {}

Advanced stacktrace:
	at com.mendix.modules.microflowengine.MicroflowUtil.processException(MicroflowUtil.java:143)

Caused by: java.lang.RuntimeException: LocalFileSystemStore:: File does not exist for key: 11
	at com.mendix.storage.localfilesystem.internal.LocalFileSystemStore.com$mendix$storage$localfilesystem$internal$LocalFileSystemStore$$getFileDocumentAsFile(LocalFileSystemStore.scala:153)
	at com.mendix.storage.localfilesystem.internal.LocalFileSystemStore$$anonfun$1.apply(LocalFileSystemStore.scala:132)
	at com.mendix.storage.localfilesystem.internal.LocalFileSystemStore$$anonfun$1.apply(LocalFileSystemStore.scala:131)
	at scala.util.Try$.apply(Try.scala:192)
	at com.mendix.storage.localfilesystem.internal.LocalFileSystemStore.retrieve(LocalFileSystemStore.scala:131)
	at com.mendix.filedocumentprocessor.internal.FileDocumentProcessorImpl.getFileDocument(FileDocumentProcessorImpl.java:68)
	at com.mendix.core.component.InternalCore.getFileDocumentContent(InternalCore.java:605)
	at com.mendix.integration.actions.microflow.ImportAction.execute(ImportAction.scala:32)
	at com.mendix.modules.microflowengine.microflow.impl.MicroflowObject.execute(MicroflowObject.java:47)
	at com.mendix.modules.microflowengine.microflow.impl.MicroflowImpl.executeAfterBreakingIfNecessary(MicroflowImpl.java:192)
	at com.mendix.modules.microflowengine.microflow.impl.MicroflowImpl.executeAction(MicroflowImpl.java:149)
	at com.mendix.systemwideinterfaces.core.UserAction.execute(UserAction.java:49)
	at com.mendix.core.actionmanagement.CoreAction.doCall(CoreAction.java:260)
	at com.mendix.core.actionmanagement.CoreAction.call(CoreAction.java:248)
	at com.mendix.core.actionmanagement.CustomActionMonitorImpl$$anonfun$run$1.apply(CustomMonitoredAction.scala:14)
	at com.mendix.core.session.Worker$$anonfun$receive$3$$anonfun$2$$anon$1.execute(ActionDispatching.scala:143)
	at com.mendix.util.classloading.Runner.doRunUsingClassLoaderOf(Runner.java:36)
	at com.mendix.core.session.Worker$$anonfun$receive$3$$anonfun$2.apply(ActionDispatching.scala:145)
	at scala.util.Try$.apply(Try.scala:192)
	at com.mendix.core.session.Worker$$anonfun$receive$3.applyOrElse(ActionDispatching.scala:139)
	at akka.actor.Actor$class.aroundReceive(Actor.scala:465)
	at com.mendix.core.session.Worker.aroundReceive(ActionDispatching.scala:135)
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516)
	at akka.actor.ActorCell.invoke(ActorCell.scala:487)
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:238)
	at akka.dispatch.Mailbox.run(Mailbox.scala:220)
	at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:393)
	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)