Your code blocks are pushing the post out too wide.
AdminCP>>Style Manager>>{Your Style}>>All Style Options>>Code Block Width (pixels)
(This value controls the width of [code], [php] and [html] BB code blocks. You may set this value to 'auto', but if you do, Internet Explorer will stretch the width of the block rather than inserting a scrollbar.)
Looks like your is currently set to 640px, try setting it narrower and it should fix your problem
Hope that helps!