exception caught with cause com.sap.engine.interfaces.messaging.api.exception.MessagingException: com.sap.aii.af.sdk.xi.srt.BubbleException: HTTP Response Received. Status Code = 500 [null "null"]

I am getting this error while testing a SOAP sender HTTP SOAP to SOAP receiver HTTP XI from web service navigator. We are in the process of migration from PI 7.3 to PO 7.5. Same web service was working fine on PI 7.3 system. Please help.