Groupwise Client cannot open mailbox files

The enduser cannot login to his groupwise mailbox. the client reports that the mailbox files cannot be opened. The post office reports error 820E on the user mailbox. This indicates that the files are locked. I have restarted the post office, but to no avail. DB maintenance on the post office and on the user mailbox (repair db, strucktural rebuild etc.) show no errors. this is a gw 8.02 installation (client and server). any suggestions would be helpful.
thanks