Mega menu drop down column organization problem

Hello

I've installed Marinelli theme for my web site and have some issues with the Drop Down menu.
I modified the file theme.inc to add a case for 8 columns (I've got menus with 4, 5 and 8 columns) and the css file primary-links.css to set the size of the menu.

But my 8-columns menu doesn't display like expected (see the screenshot).
It's very messy, I don't find the reason...

Does somebody already had this issue?
Thanks for helping.