Access denied managing two domains on single ARS server

I have ARS configured on one of our domain (, we had a request to setup ARS for an another domain. We want to have both the domain setup on the same ARS Server & both the domain appear & manage under the same ARS website.

I've added the other domain ( under managed domain using a service account of domain, Now i can view both the domains under the site but when i try creating users etc i get an access denied. the account I'm using is an administrator on both the domain & the ARS Website shows me as ARS Admin role. Is there any other permissions i need to setup to be able to administer the domain