Hi Kim, 

I believe the issue is that the Main Tax Group that the customer belongs to in Common Services - Tax Services - Tax Groups does not contain the same Tax Authorities as specified in the AR Customers- Customers - Tax Group on the Invoicing Tab of the customer record.  You'll need to add back the Tax Authority on the Tax Group in Common Services, then instead of modifiying the existing Tax Group, please create a new Tax Group with the required authorities and then change the Tax Group on the Customer Record.  

If you are still having difficulty with this, please contact Customer Support and open a Support Ticket and a support analyst should be able to walk you through this.

Regards,

David Crampton