weird ie7 behavior with two blocks

I have two blocks: one with horizontal scroll and the other with vertical. In Firefox and Chrome everything works fine. In ie7 the vertical block works fine but the horizontal takes the default stylesheet (with the default width and height, no background image etc.) even if in the view source i see that my css file is there. Furthermore ie7 freezes and crashes every time i enable the ie developer toolbar only in my site and only when i try to see the div of this block (i know ie7 is not reliable in any case but i've checked it with other sites and the problem appears only in the above described situation). In a couple of times ie7 was upset telling me that i had to stop a script from running otherwise he'll might be unstable (i guess this was a joke from microsoft but anyway that's what happened!)
When I disable the vertical scrolling block then the horizontal works fine!!! And the ie7 doesn't freezes.
I really don't know what's happening. I suspect something that has to do with jquery but nothing more than that.
Any ideas?