Sidebar sometimes moves down.

Hello,

I’ve got some problems with my site so it appears. I repositioned the sidebar with the css file. But when you press on the march archives or when you search something like polo. The sidebar suddenly goes all down. Can somebody tell me why?

My site is: http://www.noordkopwaterpolo.com/index.php

The style.css url is: http://www.noordkopwaterpolo.com/wp-content/themes/out-of-the-blue/style.css .

Thanks,
Cyril