Problem Adding User to CRM

Problem Adding User to CRM

I am the Super Admin and have set up an account for our company.  I sent invitations to 4 people to join.  Two have accepted.  The CEO is getting an email that states:  

Since you are already a part of SecuritiNet's CRM account and you are the only active user in that account, you will not be able to accept the invitation.   Delete SecuritiNet's CRM account.   Once you have deleted the SecuritiNet's CRM account, click   Join SecuritiNet's CRM account .

I tried deleting the person and adding them again and he gets the same email.  He says he has never had a Zoho account before so we can confused on what  needs  to be done.  If I follow the instructions to delete the company account, won't I have to set it up again and then add all the users a second time?  

Thanks for the help!
Mark