Hello Dahawk, and welcome to Vista Forums.
As a test, I would recommend to uninstall Norton completely to see if that may help. You can always reinstall it if it did not help any.
You might also install Windows Live Mail as a test to. If it is able to, it will import all of the Windows Mail accounts and messages by default. You can use both email clients to.
Windows Mail problems
Hope this helps some,
Shawn