HTTP Error 500 and PHP access Violation

Hello, everyone.
I’m having a few problems with my WordPress Installation. I was able to install WP without any problems but from time to time i get a

“HTPP Internal Server Error 500
Most likely causes:
The website is under maintenance.
The website has a programming error.”

this is the log line from IIS:

[
2007-01-29 17:16:54 W3SVC1 10.199.0.100 GET /blogs/itblog/index.php – 80 – 10.1.10.25 Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.1) 500 0 0
]
also sometimes i get a “PHP has encountered an Access Violation at 018DD146” on this error i get random codes. these are my specs:

WordPress 2.1
PHP 5.2.0
MySQL 5.0.15
Windows 2003 Server IIS 6

By the way, I have another WP install on the same server and it’s working fine, also I have a Gallery2 photo gallery running without any problems.

any suggestions?
thanks in advance for your help