Got a fix!

http://www.experts-exchange.com/Micr..._22729174.html

Basically, you need to change (upgrade or downgrade) the printer
drivers of your default printer. I have no idea why this causes a
problem, but I switched the drivers and no longer have the issue.

I could consistently re-create the issue by having outlook and excel
open, copying text in Excel, and then going to outlook and replying or
creating a new message. This would cause excel to close with no
warning. If I didn't have data copied to the clipboard, it wouldn't
crash. Very strange. Anyway, switching out the printer drivers for my
default printer solved the problem. I can't re-create the problem now
no matter how hard I try.

Good luck!