As you are aware that in SAP SRM, error messages are populated in the portal and it is sometimes difficult to identify the message number and it's application area although the message description is passed in the table T100.
I have come across a function module which has the list of error/warning messages populated during any process in SRM which would ease the process of identifing the details of the error messages.
FM is: BBP_PD_MSG_ADD
An external Break Point should be kept at the following line (Mentioned below) in the FM which would trigger during any process in SRM (Whether SC/PO creation) and the message number and application area can be identified.
IF <bypass_log> ISASSIGNED.
Also if it's backtracked, the exact reason for the error could be identified.