This is interesting. I remember running into a similar issue back when
I used to use Visual Studio.NET. I would do a build, then switch over
to my page and refresh. If I did it too quickly, I would receive that
same error. I believe that it has something to do with file system
locks. There are tools available from
http://www.sysinternals.com/
(filemon I believe it's called) that you can use to monitor exactly
what's being denied access to, and when. Using that tool you may be
able to understand more about what's happening when this issue arises.
-Alan