I am trying to move a user from one account to another. I have deactivated his email from the original account and i am trying to add him to the new account. It is telling me that the email is already in use. Please advise me as how to fix this. 

The user's email address is joseph.laperchia@paquinhealthcare.com

He was originally listed under the account with the email aptricia.cardona@paquinhealthcare.com. I need him to now be under the account with robert.gonzalez@paquinhealthcare.com.

Thank you.