TRUE/ FALSE in check boxes do not toggle

I created a form in Excel 2007 that uses calculations. The
calculations in the form work great on my home computer (WINDOWS 7,
Excel 2007), BUT the calculations do not calculate at work using the
same file. At work we have Excel 2007 and XP on a network. I've
tried it on one of my co-worker's computer, no luck. I sent the same
file to a friend who uses XP and Excel 2003 and it works just fine.
The check boxes do not toggle from TRUE to False. but stay on FALSE
even though the box is checked. As a result. the calculations do not
compute. Why just on my pc at work?