Typical problem I'm sure – layout

Hi everybody,
I’m running into a problem which I’m sure you’ve encountered more than once… but since I’m a newbie I really need your help on this (plus it’s time sensitive for me…)

I’ve modified the Alltuts theme running wordpress 3.5 and I’m running a plug in which is designed to create newsletter.

Whenever I click a link from this plugin (and other pages and plugins as a matter of fact) I get this page which, for the life of me I can’t figure out which file it is ..
http://dleery.free.fr/ifs.jpg

obviously the layout is incorrect since the sidebar should be on the right.. any idea why it does that ? which page should I modify ?
Thanks a lot for your help guys,