Java null pointer error from Integration Builder -> Test Configuration

Hi,

I can use a payload which works OK in Operation Mapping test of ESB, but same payload fails in IB "Test Configuration" at the same Operation Mapping step (and hence doesn't work in practice)

java.lang.NullPointerException:
at com.sap.guid.GUID.parseHexGUID(GUID.java:1015)
at com.sap.guid.GUIDGenerator.parseHexGUID(GUIDGenerator.java:111) ....

I'm not sure how to see more detail on what part is failing...any advice?