SAP Message VO201 - No longer possible to change unit

Diagnosis
You want to change the weight or volume unit. However, this is nolonger possible since workload data already exists in the databases.

System Response
The input is not accepted.

Procedure
Use the function 'F12=Cancel' to end maintenance.
Delete or archive the data, and again call up the maintenance of thecontrol data.
If no more actual data exists, you can change the units.