Just a note to let you know I've given up trying to figure out a solution.

In hope of solving the problem once and for all, I installed Excel '07 on my wife's machine that is running '10.

Remarkably, the problem still exists. Periodically, when mousing up to the ribbon all of the ribbon is completely unresponsive to the mouse. If you minimize and then restore the page, the ribbon is responsive.

Now that we've duplicated the problem with 2 different version installs, the problem cannot be with the Excel module.

I do not see how the problem could be associated with the mouse since this is the only mouse related problem with any software.

So I guess this will just remain an annoying mystery.