normal.dot changing unexpectedly

I am running Microsoft XP Professional and using Office 2003 Professional. I
am also using Outlook 2003 SP3. I use Word 2003 as my email editor in HTML.

The problem I am having is that the normal.dot gets corrupted unexpectedly.
I use email signatures and some times they are not there.

I have backed up the normal.dot and when this happens, I restore normal.dot
from my backup and everything is fine.

Any help would be greatly appreciated.