I've tried this a couple of times. I wanted to try out the new FreDiablo theme, which does not have icons for web or contacts. So I went into the control panel and under panels, turned these two off. The first time I did it, it said something to the effect of "Requires two plugins" and the ok button was grayed out.

The second time I tried it, that message did not pop up, but the ok button was still grayed out. Why is this happening? What are these two plugins? Do I need web and contacts?

Edit: Disregard, I found the answer...