Diagnosis
You have tried to assign a value to variable &V1& (name &V2&), whichmeans that this variable is used on the left side (assigned value side)of a formula in the control table for the representative list of rents.

System Response
This variable was not created by SAP. It originates from acustomer-specific enhancement. If it is used on the right side of aformula, its value is determined by calling the customer-specificfunction module (user exit). Since the variable therefore represents afunction call, its value cannot be changed by assigning it a new value.

Procedure
If you have determined the value using the user exit function modulebut wish to change it, you can do this through the use of a helpvariable which you assign to the variable.