What causes this issue?

The different priority routines and their respective values are shown.

System Response

Priority value ' ' means that the current record has no priority, namely
it should be deleted from the database.
Priority value 'X' means that the current record has priority, namely
it should not be deleted from the database.
Priority value 'I' means the priority is irrelevant for the record,
namely it is not important whether the record will be deleted from the
database or not.

How to fix this error?

Contact SAP in case of problems.

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.