Here's what's happening. There is a shared workbook that is protected. When
we open the shared workbook and click in any cell, Excel seems to freeze.
When we move the mouse it acts as if you are holding down the left mouse
button and is selecting a range of cells. You can't close Excel or do
anything else. You must CTRL+ALT+DEL to close Excel. Then after that, until
the system is restarted, every Excel document that is opened will do the same
thing.

I can't seem to figure out if it's a network, Excel or protection problem.
Any ideas?