Hello,
Just installed few days ago K2 2.5.5 on joomla 1.5.23, but I have few conflicts at the admin page.
When I click on parameters it dose not popup but instead it's open the parameters page over the admin page Untitled-4.jpg - 0.12MB

Also, when I enter to K2 the joomla admin top menu is disabled and I can't click on anything, only on the K2 menu (items,cat etc...)

Thanks
Ran

I have finally spotted the issue. I have used the plugin "System - Drag n Drop Admin".