Issue with SAP PO 7.5 Rest Adapter to Function Modul in ERP System

[stephan_kohler3]

Dear ladies and gentlemen,

we run now in an issue, after we migrate our SAP PI 7.31 Double Stack to the SAP Java Single Stack 7.5. The issue is, that the ERP System return an http code 406 back to the SAP Java Single Stack 7.5, before we use the SAP PI Dual Stack 7.31 we get the http code 200, and the Rest Adapter Scenario works without any issue.

In the meantime I compare the Scenarios between the both SAP PI/PO Systems, and the Scenario are total identical, therefore I assume the issue should be on the target system.

Attached the errors which we see in our SAP PO 7.5 Single Stack. Therefore if you can help to solve the issue would be helpful.

Scenario is:
Incoming Request via RestAdapter -> PI/PO -> Request send via RestAdapter to ERP System.
The Service http Link for ERP is:
a.) http://Hostname:Port/serrala/corecomp/fmcall/FuctionModul

The answer back is always the same in SAP PO from SAP ERP:
Server returned code: 406
HTTP error occurred: Not Acceptable
MP: exception caught with cause com.sap.aii.adapter.rest.ejb.common.exception.HttpCallException: HTTP POST call to http://Hostname:Port/WebService/RFC - FuctionModul not successful. Not Acceptable
Exception caught by adapter framework: HTTP POST call to http://Hostname:Port/WebService/RFC - FuctionModul not successful. Not Acceptable
Transmitting the message using connection REST_ http://sap.com/xi/XI/System failed, due to: com.sap.engine.interfaces.messaging.api.exception.MessagingException: com.sap.aii.adapter.rest.ejb.common.exception.HttpCallException: HTTP POST call to http://Hostname:Port/WebService/RFC - FuctionModul not successful. Not Acceptable

Thanks for your help
Kr Stephan