SAP Message WAHD004 - Could not set lock on table WAHD(-OVAL)for plant &1

Diagnosis
The system was unable to set a lock on tables WAHD or WAHD_OVAL.
This could be caused by a process that is currently running, or becausea user is processing a required record at the same time. The system wasunable to load thealternative historical data
(AHD) for the whole plant
.

Procedure
Release all locked records for the plant and start the program again.