I've recently faced some problem login in to Plesk,
When I try to login to plesk the following error with occurs:
Fatal error: Access is denied. (Error code 5) at Connect to pipe in C:\Program Files\SWsoft\Plesk\admin\plib\common_func.php3 on line 3072

Searching on the net have not help me and I'm also unable to afford Plesk's expensive support on this issue, and unfortunately they don't have and up 2 date KB or forum, and you can even find 2 years old unanswered questions there!

I desperately need your help guys...

I've also attached a screen shot to this post.

Your MySQL server is acting up. How exactly now clue but you need to make sure it's running.

I upgraded to Plesk 8.1.1 and users can login to their Plesk account.
But unfortunately after the upgrade, plesk name server service (Bind DNS service) didn't start, and as we live in Iran and ISPs don't use live DNS resolving I didn;t notice this problem.
The next work day, after receiving customers complains, I found out the problem, and after a research on the net I realized that the only way to get rid of this problem is to change the DNS Service, I did and now the DNS server is working properly too, and I'm waiting to see what would be the next problem with Plesk