Windows Service: Access Denied

[Archdeacon]

(Xp Pro Sp2, Administrator account) After upgrading my regular anti-virues software, the new version renders its service incapable of being reset from Automatic to Manual. I need this setting as I run a CIM CommandLine EventConsumer which runs a script automatically on detection of Event 4201 (Network Connection) and starts this service. I do not need it running when i am not online as it just slows everything down.

Presumably some Reg DWORD has been changed somewhere but can anyone tell me where to look please?