Exception: Content is not allowed in prolog. while using excel importer module

When using the excel importer module I'm getting the following error: Content is not allowed in prolog. Followed by: 

com.mendix.systemwideinterfaces.MendixRuntimeException: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.
	at com.mendix.integration.importer.xml.XmlImporter$$anonfun$importStream$2$$anonfun$apply$1.apply(XmlImporter.scala:77)

Caused by: org.xml.sax.SAXParseException: Content is not allowed in prolog.
	at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
	at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
	at com.mendix.integration.importer.xml.XmlImporter$$anonfun$1.apply$mcV$sp(XmlImporter.scala:52)
	at com.mendix.integration.importer.xml.XmlImporter$$anonfun$1.apply(XmlImporter.scala:52)
	at com.mendix.integration.importer.xml.XmlImporter$$anonfun$1.apply(XmlImporter.scala:52)
	at scala.util.Try$.apply(Try.scala:192)
	at com.mendix.integration.importer.xml.XmlImporter.importStream(XmlImporter.scala:52)
	at com.mendix.integration.importer.xml.XmlImporter.importStream(XmlImporter.scala:31)
	at com.mendix.integration.internal.InternalIntegrationImpl.importStream(InternalIntegrationImpl.scala:294)
	at com.mendix.integration.actions.microflow.ImportAction.execute(ImportAction.scala:48)
	at com.mendix.modules.microflowengine.microflow.impl.MicroflowObject.execute(MicroflowObject.java:47)
	at com.mendix.modules.microflowengine.microflow.impl.MicroflowImpl.executeAfterBreakingIfNecessary(MicroflowImpl.java:192)
	at com.mendix.modules.microflowengine.microflow.impl.MicroflowImpl.executeAction(MicroflowImpl.java:149)
	at com.mendix.systemwideinterfaces.core.UserAction.execute(UserAction.java:49)
	at com.mendix.core.actionmanagement.CoreAction.doCall(CoreAction.java:260)
	at com.mendix.core.actionmanagement.CoreAction.call(CoreAction.java:248)
	at com.mendix.core.actionmanagement.ActionManager$1.execute(ActionManager.java:168)
	at com.mendix.util.classloading.Runner.doRunUsingClassLoaderOf(Runner.java:36)
	at com.mendix.core.actionmanagement.ActionManager.executeSync(ActionManager.java:172)
	at com.mendix.core.component.InternalCore.execute(InternalCore.java:414)
	at com.mendix.webui.actions.client.ExecuteAction.execute(ExecuteAction.java:144)
	at com.mendix.webui.requesthandling.ClientRequestHandler$$anonfun$handleRequest$1.apply$mcV$sp(ClientRequestHandler.scala:312)
	at com.mendix.webui.requesthandling.ClientRequestHandler$$anonfun$handleRequest$1.apply(ClientRequestHandler.scala:302)
	at com.mendix.webui.requesthandling.ClientRequestHandler$$anonfun$handleRequest$1.apply(ClientRequestHandler.scala:302)
	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)

What I'm trying to acchieve is uploading an excel file with a batch of new users so account will automatically created for them. The domain model exists from:

Entity Account:

• FullName
• Email
• PhoneNumber
• Department
• Jobtitle
• Password
• Name (username)

Entity AccountXLS -> * - 1 ClientXLS_Account (generalization with ExcelImporter.TemplateDocument)

Entity AccountTemplate -> 1-1 AccountTemplate_Account (generalization System.FileDocument)

Does anyone know how to fix this error?