SAP Message 26255 - Document is being processed by user &

Diagnosis
You are trying to open a document that is locked

System Response
Another user has set the status type O for the document you wantto open.
The status type O reserves one or more originals of thisdocument for processing. This causes the document info record to belocked from other users.

Procedure
If the status network allows it, you can set a new status. Check firstto ensure that the other user has finished processing the document.