Some plugins break the WPMU completly

Hello everyone!

I have a very serious issue that stops me from fully developing my Multi Site project.
Some plugins that I need to use (like qTranslate) couse me to get locked out of the blogs where they are activated.

This is what happens:
01. I download the plugin, install and activate it
02. When I click ACTIVATE I get logged out of my blog
03. When I login again (at the moment of the login the URL is OK) I go from company.expromo.pl/wp-admin/ to expromo.pl/wp-admin (this is my main blog url) and get a ?c=1 after the URL. So the full URL looks like this:

http://www.expromo.pl/wp-admin/?c=1

04. I get locked out of the blog where the plugin is activated (is always redirects me to the main site) until I delete the plugin.

I'm attaching a screenshot of how this issue looks in real life.

The strange thing is that on some test installations these issue doesn't happen - how can I debug this? What can couse this kind of behaviour?