What is your current default for outgoing messages?
You can try this:
Open the Default Programs applet, which you can access either from
the Start menu or via the Control Panel, then click the first item:
"Set your default programs."
After a few seconds, a list of programs comes up. Click on "Windows
Mail". If it doesn't respond with "This program has all its defaults"
then fix it by clicking on the option indicated by the first green arrow.
