Use importStream after conversion

After converting an App from Mx5.21 to 6.5.1 the importXmlStream needed to be replaced by importStream because of deprecation. The importXmlStream function mapped an XML without problems to the domain. However, the importXmlStream function returns the following error:

java.lang.ClassCastException: org.apache.xerces.dom.DOMXSImplementationSourceImpl cannot be cast to org.w3c.dom.DOMImplementationSource
    at org.w3c.dom.bootstrap.DOMImplementationRegistry.newInstance(DOMImplementationRegistry.java:187)
    at com.mendix.integration.xml.SchemaLocationResolver.<init>(SchemaLocationResolver.scala:16)
    at com.mendix.integration.importer.xml.XmlImporter.com$mendix$integration$importer$xml$XmlImporter$

A search on the internet does not provide useful information, so maybe someone here has an idea. Do I need to add something to the WSDL or is there maybe an incompatible java libary?