Thanks for the suggestions!
It would appear that the folder in question is something created by TestComplete during install and it had somehow got itself all locked up yesterday.
Tried to view the folder this morning and Explorer locked up and stopped responding.
Rebooted my machine and the folder had gone.
So tried to install TestComplete again and it worked fine. Once complete, that folder was back again (with a time stamp of during the install) and has two DevExpress DLL's in it.
No idea why it decided to lock up. Never happened when I've upgraded before ...