Windows Live Mail – “recipoients not valid”

I cannot send email to any of my contacts - receiving emails OK.

Message panel below appears when Send button pressed.

 "The message could not be sent.

Some of the recipients for this message are not valid.

Please verify the names."

This happens for e new email or when replying. With 1 addressee only.

Addresses were checked and valid.

I ran the Live Essentials repair via Control Panel and no errors detected.

Thanks,

Kevin