i assume this message comes from MS office?
can you confirm the version of office and windows?
does the user see his own user as the one with the lock?
what do you see with the command " vserver locks show -fields sharelock-mode,type,oplock-level,client-address,path" ?
also adding here some resources for yourself to troubleshoot with:
see http://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.cdot-famg-cifs%2FGUID-F6CA9D0F-B205-4E92-A429-C4E8D709B825.html if you want to break a lock for a user after you seen one with the earlier provided command.
see https://kb.netapp.com/app/answers/answer_view/a_id/1070644 for a known issue.
if the lock is for the same user itself. it could be an orphan session that still hold the lock. if it happens after a known network disconnection (hibernate, move between wireless point or from wireless to Ethernet). it could be that reducing the timeout will improve the user experience (900 sec is the default()
cifs options modify -vserver VSERVER -client-session-timeout 900
Gidi