Diagnosis
You want to enter a previous status for a status (such as work request- WR).
Each status is assigned to a status type (such as primary status - P).The status type controls, for example, whether you can enter a previousstatus for a status.
The status you are processing at the moment has a status type whichdoes not allow a previous status (for example, primary status).

Procedure
Check the status type.
If you still want to enter a previous status, the status type must bechanged via settings in Customizing (Document management -> Controldata Document status). Otherwise, you cannot enter a previous status.