Can not Add users in Zoho Campaigns

Can not Add users in Zoho Campaigns

Hello,

In our organization we have created 2 Zoho users/accounts.
We work together in CRM without problems.

We were now evaluating Zoho Campaigns App (individually)....

I was trying to add the other user in my Zoho Campaing....but i am allways getting the error:

This email address has been already used in some other organization. So you cannot add/invite this user

If he tries to Add me he got also the same message....what is wrong?
How i can solve this?

Thanks,