An MSSQL 6.5 server configured for Mixed security had the MSSQLServer and
SQLExecutive services logging in under the local system account. Using NT Server
Manager, I changed the startup parameters so that both services would log in
under a domain account.

Problem: when the services were stopped and re-started, the security had changed
from Mixed to Standard. In addition, SQLExec tasks started to fail.

The domain account I used has the rights for logging in the SQL services; it`s being
used without problem on a number of our other SQL servers (although all of these
are running Standard security). The account is also a member of the Domain
Administrators group, which I thought automatically mapped to sa under Mixed
security, so why the failed tasks?

Can somebody explain where I might have gone wrong?