IS-OIL - Invalid ROLLBACK WORK in an update function module

Hi,

I am getting this dump which points to CL_PO_HEADER_HANDLE_MM========CP.

In the system Update Records (SM13) there is an error for transaction O4NM for custom function ZOIJ_UPDATE_RELATED_DOCS.

I have no experience with OIL module so any advice on how to go about tracing the cause of this error would be appreciated.

Regards,

Warren.