If you have a guest account in a client's %BRAND_OFFICE_365_SHORT% tenant and are experiencing issues when trying to enter ...

If you have a guest account in a client's %BRAND_OFFICE_365_SHORT% tenant and are experiencing issues when trying to enter that client's %BRAND_OFFICE_365_SHORT% admin center from PAC, delete the guest account in your client's tenant. After deleting, you will now be able to enter the client's %BRAND_OFFICE_365_SHORT% admin center through PAC.