SAP Message TT190 - Parameter &: Only variable & & is permitted

Diagnosis
The export parameters returned can only be assigned to 'V'variables (&V01..&V20) or to export parameters (&E01..&E05).

Procedure
Only use 'V' variables (&V01..&V20) or export parameters(&E01..&E05) in the field 'Return in'. To assign these values toother variables, use the 'SETVAR' function in the function screen.