Error deactivating user

Error deactivating user

Hello,

I am getting the below error when I try deactivating a user, I have disabled all the apps assigned to the user except for books/invoice  

 ****Status cannot be changed. The user's credentials are already being used for Integration with Zoho Projects***** 

Steps taken
>> I have gone to Zoho Projects to check for any integration and I don't see any integration between Zoho project and Books/invoice
>>I have gone to Zoho CRM and there is no integration
>>Checked to be sure that the user is not an admin and does not have admin rights 

Is there something I am missing?
Please assist?

Regards.