When I send a reply message to certain email addresses, I get an error message.
The error is one of the following two:
Insufficient Memory - 108
or
Unknown Error - 8796

This only happens when I reply to a very few specific recipients.

I have no problem receiving email from them and no problem sending new messages to anyone.

Office for Mac 2011
Ver.14.2.4
iMac 21.5 in. OS X 10.8.2