YMSEG is a standard internal table used in import and export of function modules.
if you search SAP notes on YMSEG then you get about 230 hits.
Unfortunately the info given is by far not enough to tell you the reason for this error.
The number from the error explains just that it is one of the sales set Components
But you need to describe the process and what changes you eventually did compared to standard process. Only then we might be able to help you further.