Tooltips in Win 2k/XP

I've just run into a problem and I've no idea how to fix it.

I've written a simple user control that is basically just a text box with some added functionality.

When I set the Tooltip for the control, the tooltips don't seem to work in WinXP.

I'm writing the app in 98 and they work fine here. In XP, sometimes they appear and other times they don't. Very strange. I tested the app on a Win2k machine and they don't seem to come up at all.

Does anyone have any idea what's going on here? I'm sure it's a problem with MS since there is no code in implementing a tooltip for a user control but I can't find any fixes or patches to handle this.

Thanks for any help anyone can give!

Sean