Could not put all messages into process

What causes this issue?

You can only put a notification in process if they have the status
"outstanding" or "reset".

System Response

All the notifications with the status "outstanding" or "reset" are put
in process, all the other notifications remain unchanged.

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.