Cost assignment type &1 is not allowed

What causes this issue?

You have assigned costs or revenues to a cost objects of type &v1&.

System Response

Cost assignment type &v1& is not allowed.

How to fix this error?

Use a cost object of another category such as cost center or order.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.