Then you will need too clear the outbox using this utility. http://www.oehelp.com/WMUtil/Default.aspx
Follow ALL the instructions to make the function you need
available. Particularly those in the red box.
The root cause of you problem is likely to be an incompatible
POS antivirus program such as Norton or McAfee which will
need uninstalling and replacing with a free alternative such as
Avast. Which ever AV you use the email scanning component
should at the very least be disabled and better yet omitted
at install time.
