I was working on a project using Visual Studio.
I had a post build event that updates my assembly in the Global Assembly cache.
I noticed that when i complie my project i get Access denied to the GAC ans sometimes it runs ok.
After doing some research i came across this solution at
global cache security
which suggested using the command from cmd:
CACLS %WINDIR%\assembly /e /t /p [DOMAIN|MACHINENAME]\useraccount:R
and that did work for me ..
But you can see some other suggestions here at this
post
Although the post suggested disabling index services

which some people said it worked for them..
hm....