Calendar on userform is blank

I wrote a wizard that has been in use for almost 2 years now with no
problems, in excel 2003. I have the Calendar Control 11.0 on a form to enter
dates. Recently, one of the users has been getting a blank calendar. The
calendar works when you hit a button, but you can't read the month or day on
the calendar itselft. Everyone else is running fine, except the one computer.

I checked that the reference to the calendar is there, and it is. I even
registered the control again, but it is still blank. Any ideas?

NOTE:
I recently installed a trial period of Excel 2007 on my computer only, and
have opened this wizard with excel 2007. I noticed the control reference on
my computer automatically changed to "Microsoft Calendar Control 2007". I
thought this might be the problem, but no other computers are having a
problem, and there are about 7 of them. The reference on those computers is
still Microsoft Calendar Control 11.0.

thanks,
Steve