At home, I would use the excellent LockHunter, but I am work and not allowed to install software, and LockHunter does not seem to have a portable version (feel free to correct me, as that would be the preferred answer).
One app has a supposedly locked directory; I have closed everything that I think could possibly be accessing it, to no avail.
At home, I would simply fire up Lockhunter and select "What is locking this file?" to know which app I have to terminate.
I could reboot, but have too many apps still open, and it is a major pain to reboot, passphrase, magic number for security dongle, password, then re-open all of those apps.
The company firewall prevents me viewing freeware/shareware sites. Is there any gratis Windows app which will tell me which app is locking a file or directory?
[Update] I have found this page an dwill be working my way through it. I will post my findings