Diagnosis
During the returns dialog, you enter a selection value with which (inconnection with selection type) the system determines the number of theclearing document. This information is determined using Event 255,provided the selection type you specified does not refer to OPBEL, asis here the case.
However, the system was able to find a function module at Event 255.

System Response
You can only enter returns that have a selection type referring tofields OPBEL or CHECF.

Procedure
If you want to use other selection categories, you need to enter asuitably programmed function module under Event 255 in the relevanttables.