SEC 5.2 will not install - interactive logon error...aaaarrrgggghhh!!

I am running 2 x 2008r2 servers.

The database is 2012 on one of the servers.

SEC 5.2 on the other.

Both are part of a larger Domain.

I have setup the service accounts as per article KB113954. "SophosManagement" and "SophosUpdateMgr"

I first installed the database on one of the servers successfully. Yeah!

But...when installing SEC 5.2 on the other server, I get the following error when I enter the credentials for the database.

"The specified account does not have interactive logon rights on this machine."

When I change the service account to have local administrator rights, it will install successfully.

The documentation and best practice says not to give service accounts administrator rights. Users rights is ok...apparently.

These accounts are set as "logon as a service", and these type of accounts are not suupposed to have interactive logon rights.

So what gives?

Any ideas??