Nan. I also followed the invitation link and subscribed. I couldn't
post until my group membership was activated. To do this, I had to
"create an account", but that really just meant entering my regular
email address (not a gmail address) and a password. Then I had to
wait for a verification email to be sent to my email address, and I
had to click on the link there, before my membership was all
complete. Now I can post. Maybe you tried again under another email
address before you finished the member activation process?