Sharing violation and background process

I keep getting a sharing violation error when trying to save documents
in DW8. I've searched this group, and found nothing that seems to
solve my problem. This just started happening today.

I am working off a local copy of a site that resides on the server.
Check in/Check out is enabled and I have checked out the files. Some of
the files are newly created and have not been put on the server yet.
The files in questions are physically on my C:\ drive, not the server.
I can work for awhile, but after a half hour or so I start getting the
sharing violation message when I try to save. I then try to put the
files back onto the server (with put or check in) but can't do that
either. I've tried restarting DW, but no luck. I have admin rights on
the computer.

Any thoughts?

thanks,
Gary