The assignment of object & to level & does not exist

What causes this issue?

The assignment does not exist in the classification system or is
different.

System Response

The status for this object is set to "Checked with errors". This object
cannot be reclassified until the error has been eliminated.

How to fix this error?

Check and correct the assignment if necessary. Then perform the
reclassification check for this version or object again afterwards.
If this does not solve the problem, please contact your system
administrator.

Error message extract from SAP system. Copyright SAP SE.