SAP Note 21383 - ME55: Query for valid sort indicator

Symptom:

When you enter invalid sort indicators (that are not numeric), program rm06bf00 encounters an error.

Cause and prerequisites

Check for entry was missing.

Solution
Correction in RM06BF00 Event AT SELECTION SCREEN
....

*--- Sortierkennzeichen ------------*

if p_srtkz cn '0123456789'.
message e309.
endif.
Please maintain message 309 for message class ME with the following text in table T100: "Please enter valid sort indicator."