SAP Message PU001 - &1 is not a valid client

Diagnosis
The value &V1& is not a valid client because it is not contained in thetable for all clients, T000, or because it is not only composed ofnumbers (0 bis 9). Valid client names are 3-digit numbers (000 to 999)that are entered in table T000.

System Response
The function terminates.

Procedure
Only perform this action for a valid client.