Gateway configuration for Paginated Reports

[scurrp]

Hi, 

I'm stuck trying to determine if what we need to do is possible and we've got the configuration wrong.
Scenario:
Paginated Reports call stored Procedures on a database to deliver report content. 
The Gateway is installed on its own Server and runs as a Domain Service Account (AcctA).
Connections to the database work when the gateway connects to the data base as AcctA. 
What we want to do is connect from the gateway to the Database using a different domain service account (AcctB).
AcctA and AcctB have the same permissions on the DB at this point in time.
When we configure the Gateway to connect to the database as AcctB the following message appears.
 

The gateway is not configured to use Kerberos (see below) but the error above indicates an impersonation issue.
For a sanity check a new gateway was installed on a seperate server and returns the same error message.
Is there something outside of the Gateway that we need to set or is the proposed scenario not possible to be configured this way.
Does AcctB need to be a named SQL user and not a domain user?
Troubleshooting in made complex as Kerberos / Gateway / DB Security are managed by different teams.

Thanks in advance for any assistance.

[lbendlin]

You don't really want the gateway service to run under your service account.  Reinstall the gateway and let it use the default NT SERVICE\PBIEgwService account.  

The credentials for the connection are independent of the credentials used for the service.

[scurrp]

@lbendlin Your second point is the problem I'm trying to solve.
Are there permissions granted to NT SERVICE\PBIEgwService that would not be applied to the service account we're running the gateway as?

[lbendlin]

The account that the gateway is running under needs to be able to write to disk on the gateway cluster member. The account listed for each connection needs to be able to read from the data source.