How are you trying to "join"?
The first thing to do is to go to your cousin's profile, then under the "Actions" button select "Add to Family Group". When your cousin accepts that request, then you should be able to connect and work on your joint family tree.
It seems there might currently be some problems with displaying the message which should display, but doing the "Add to Family Group" should get the two of you into the same family until you actually have entered "profiles in common" (e.g. grandparents, or whatever the 'connection' is between you).
I received the following email
I've added you to our family tree.
Dear John,
I've added you to our family tree on Geni, a website that helps families create and share their family tree and stay in touch with each other.
View our family tree
when I click on the link and go to the page with Are these both you?
Yes, Join Spencer's Tree this is when I get the message
John - Given your description of what is happening, it is almost certainly a Bug. A Basic Member cannot create a Ticket, but should be able to Create a Bug report over in Help. However ...
How long has the problem been going on?
I am thinking, if it has been less than a day, try it a few more times. If it has been several days, it may be time to try tagging our chief debugger. What do others think?
Hi John, I work for Geni and would like to help. I'll follow up with an Inbox message ( http://www.geni.com/threads ) because I'll need to ask you about your email address, which is best not posted publicly due to spammers.