Ok, I found the problem
I am using WPMU members and BP 2, I also use a myriad of other plugins so it was driving me crazy … The issues was pretty simple to fix in my case, YOU MUST ensure that you have activated the REGISTER and ACTIVATE pages in your Buddypress settings (Settings>>Budypress>>Pages)
Once I activated these the Invite me emails work fine are pointed to a registration form with a confirmation of the invite to a group.
Hope this helps !
Regards
Richard
if you look at my site please, I know where the favicon is, this is inside my page …. always4ever.co
Thanks
Richard