You might try uninstalling Bullguard temporarily to see if that was the cause.
If that fixed the problem, you can replace Bullguard with a more compatible
antivirus. The free ones work well enough:
AVG free edition:
http://free.grisoft.com/doc/5390/us/frt/0?prd=aff
or
Avast free edition:
http://www.avast.com/eng/download-avast-home.html
With either of those, during the install phase you must select custom
install, and then deselect the email scanning option.
Another option is to upgrade to the newer Windows Live Mail program.
It will automatically import all your WM accounts, settings, emails, folders,
rules, etc. Contacts may have to be imported manually, but that is
easily done.
http://get.live.com/wlmail/overview