Written
I think that the "Invalid address:" message comes up in a couple of circumstances:
a) If the From Email Address in the Email action doesn't match the Admin address in the Site email configuration*.
b) It there is a missing or broken From Email address (or possibly Reply To Email address).
b) It there is a missing or broken From Email address (or possibly Reply To Email address).
* For the Site Email Configuration go to Site Admin | Site | Global Configuration | Server | Mail Settings (update the "Mail from" field) )
