Allocation table relevance indicator incorrect

What causes this issue?

A data conflict occurred
You cannot delete the indicator for allocation table relevant if an
assignment to an allocation table exists.

System Response

The program can no longer restore the original state. For this reason,
you cannot save the purchase order document.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.