Try to disable email scan, internet filter and download scan in McAfee virus scanner at least temporarily to see if this fixes the problem.
Disable the above
Reenter your Outlook express info
Restart
If this fixes the problem
you may want to switch to another virus scanner
from everything i have read Mcafee doesn't play nice with outlook express or outlook for that matter
AVG has a free virus scanner that scans incoming mail as well
I use this one and haven't had any problems
http://free.grisoft.com/freeweb.php/doc/1/lng/us/tpl/v5