[SOLVED] mootools error code=0 on ie only --> messed-up layout and buttons

Hello
My website works just fine on safari chrome or firefox but whenever I test it with internet explorer everything is just messed up.

http://www.monparispascher.com/remis...n-des-plantes/

On IE, my articles won't display entirely and will be floating on the right of my page. Moreover my buttons (css3 buttons plugin) won't display correctly (red-filled big rectangles instead of buttons).

IE tells me there's a problem with "mootools for dropdown" (error code=0) in my mootools.js. My deduction is that I have a mootools jquery conflict with IE but I just don't know how to fix it (I am quite new with webmastering...)

Also I don't know if it can be connected but my dropdown menu won't always work well or at all with any browser :
1. the menu "par arrondissement" won't just drop
2. the menu "par arrondissement" will drop just once or twice and then won't anymore.

Can someone please help me ???
Thank you