SAP Message VN025 - Output & for medium &, partner function & is not defined

Diagnosis
You have selected a combination of output and partner function whichhas not been defined.

Procedure
INCLUDE NA_EINGABE_PRUEFEN
This is a warning message. You can proceed by pressing ENTER.
To prevent the warning message from appearing again, assign therequired partner function to your output type in table TNAPN.
IF &DEVICE& = 'SCREEN'
Execute function
ENDIF