I tried again as you said, but it still complained. What I ended up doing was to send the invitation to your gmail address without the two dots (as it's an alia

I tried again as you said, but it still complained. What I ended up doing was to send the invitation to your gmail address without the two dots (as it's an alias for your original address), and apparently it worked. I also emailed you the invitation code they generated, from my personal email.