Deleting old entries in table RZLLITAB failed with sy-subrc = &1

What causes this issue?

An error occurred while accessing table RZLLITAB.

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

System Response

The system attempts to delete old entries for the RFC group
'parallel_generators' from table RZLLITAB. The reason for why the
access failed may be, for example, that access to this table is
currently blocked by another user.

How to fix this error?

Transaction RZ12 (CCMS: RFC Server Group Maintenance) allows you to
maintain table RZLLITAB manually. If access to table RZLLITAB is being
blocked by another user, you are told this directly after calling this
transaction.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.