When I choose Add Project" in the CRM I get this message

The client user(s) [XXXXXX] were not added because users with these email addresses have already been added to another client in Projects. Users with the same email addresses cannot be associated with different clients. If you would still like to add them to your project, re-invite them using an alternate email address.

What does this mean as I only have 1 test user?

I want to 

1. Convert lead to contact/deal

2. Create project for the contact

3. Work with the client through projects

Thanks