Hello,
How did you set up your menu item ? The main group’s width must be set and also the sub group.
For example, you have menu structure like this.
- Menu Item X
- Sub Item 1
- Sub item 2
- Sub item 3
- Sub item 4
- Sub item 5
You must set width for Menu Item X in Sub menu with, and set width for one of Sub menu item in Sub menu column width like this http://wiki.joomlart.com/images/b/ba/Megamenu-userguide-megamenu-parameters.png
If you set width Menu item X is 1000 then width of one of sub menu item must be 200, (200×5=1000)
Hope this helps, or else PM me your site URL and admin account ( with this link forum) then I shall check for you