Many people in other forums are always complaining on how to disable their on access scan in McAfee anti-virus. They said that everytime they click the Disable On Access Scan fuction, nothing happens. So this is how you do it.
1. Open up the Virus Scan console. (As admin on vista)
2. Open up the properties for the Access Protection thing.
3. in the bottom, there should be a box that says: Prevent McAffe services from being stopped. un-check that box.
4. now close the Virus Scan console and right click the McAffe icon on your start menu and click disable On Access Scan.