Backorder processing status (&1) does not allow any changes

What causes this issue?

Changes cannot be made in the current
<DS:DE./SAPAPO/BOP_STATUS_BOP>status</> of backorder processing.
Changes cannot be made if backorder processing
is not completed,
was only performed as a simulation (in this case, temporary quantity
assignments are not written), or
has already been updated.

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

System Response

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.