com.ctc.wstx.exc.WstxParsingException: Illegal processing instruction target (xml)

I try to connect two Mendix applications by a webservice. Unfortunately I get an error message which I couldn't resolve after many tries: com.mendix.modules.microflowengine.MicroflowException: Failed to copy a message at IPs.GetIPsInProcess (CallWebservice : ''IPListing'') Advanced stacktrace: at com.mendix.modules.microflowengine.MicroflowUtil.processException(SourceFile:157) Caused by: com.mendix.systemwideinterfaces.MendixRuntimeException: Failed to copy a message at com.mendix.ji.a(SourceFile:24) Caused by: Failed to copy a message at at at at ... Caused by: com.ctc.wstx.exc.WstxParsingException: Illegal processing instruction target ("xml"); xml (case insensitive) is reserved by the specs. at [row,col {unknown-source}]: [1,389] at at at ... I checked securities on both sides, the webservice definitions and the XMLtodomain_mapping but I have no ideas what is wrong. Does anyone has a suggestion what to do?
2 answers

No direct solution but a common approach is:

  1. Check the ws-doc by calling the server servername/ws-doc/ so you can see the server is running and webservices are available
  2. Use a tool like SOAP-ui to construct a webservice call manually and send it to the server to check the result. Some knowledge of SOAP/xml is required
  3. Set logging of webservices (both sides) on trace. With some luck you can copy a soapmessage and paste it in SOAP to get more insight details.

I found the answer by running both versions locally.

This cryptic error message is given when an attribute to be exported is not optional and has value 'null'.

Solution is to redefine the sending webservice, specifying fields that can be null to be optionally.