For the problems Norton antivirus programs sometimes cause, just disabling
the Norton program is not enough. You have to uninstall it, then run this
cleanup program:
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http://service1.symantec.com/SUPPORT/tsgeninfo.nsf/docid/2005033108162039>
You may then also have to remove your email account under Windows Mail,
then restart Windows Mail and create the account under Windows Mail
again. Many versions of antivirus programs from McAfee and a recent
version from Trend also have such problems, and the problems are often
slow to show up.
Also, download and install this fix, with Windows Mail not running:
http://support.microsoft.com/default.aspx/kb/941090
Although it's labelled as for mail stuck in the Outbox, it also works in
other folders. If you don't know whether to use the 32-bit version or
the 64-bit version, try the 32-bit version first.
If this solves your problem, you may want a replacement antivirus
program. I recommend either the avast! or the AVG program,
either one with a custom install that tells it to leave out the part
that scans email.
http://www.avast.com/eng/avast_4_home.html
http://free.grisoft.com/doc/5390/us/frt/0?prd=aff