Control key & cannot be used here

What causes this issue?

You wish to change the control key for quality management in
procurement. Only the following changes are allowed:
Set current control key &V2& from material
Set existing control key of item &V3&

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Enter one of the allowed control keys.

Error message extract from SAP system. Copyright SAP SE.