Class type & : the status of class & does not allow assignment

What causes this issue?

You want to assign objects to a class or find objects in a class.
However, the class does not allow you to do this due to its status.

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?

Check whether the class status can be changed. If it can, set the
status to "released" in class maintenance.
<DS:TRAN.CL02:>Proceed</>

Error message extract from SAP system. Copyright SAP SE.