Children clipped in drop down menu

I had a client request drop-down menus last minute a couple days before we're launching a site. Normally I manually code them but given the time pressure I thought I should give nice menus a try.

I've installed them and enabled them in a block, but haven't begun to style them or anything like that. The top row displays normally, but on mouse hover only a sliver of the child item appears below. There is nothing below the menu but white space at this point so nothing is 'covering' the menu. I've tried placing the menu in numerous locations around the page and the same thing happens everywhere.

Is this a common problem? I can't find any obvious place to fix it.

Please help! This problem is the same in Firefox 3 and Safari 4. Haven't had a chance to test in other browsers.

Take a look at the attached image.

Thank you!