WordPress MU

I have this problem (http 500 internal Error)
I can not access to my wordpress Admin http://www.mysite/wordpress/wp-admin/

Could somebody help me ,solving the problem?????
thanks

Shouldn't there be a ".com"?

You mean that may actually be Mark Goldson, the owner of the mysite.com domain? :)

As noted in the 500 error, you should be checking your webserver's error logs to see what's in there. That should always be the first step when trying to solve an issue.

Required reading linked to from the readme file as well:

http://codex.wordpress.org/Debugging_WPMU

You may also want to skim the readme file and make sure that 1) You;ve read all of it and 2) You've followed all of the steps required. If you're installing wpmu using a subdirectory and posting here using mysite.com, chances are you may have missed a few steps in there.