I had the problem of the McAfee real time scanning not staying on and fixed it by clicking on the McAfee icon to open it up. Then going to help in the top right hand corner. Then clicking on the link going to the McAfee support website. Then you can click 'get support'. Then click 'go to technical support'. I'm not sure what fixed my laptop but I used the virtual technician and then looked at the faq and used the article:
Document ID: TS100903 entitled "Your computer is at risk: Real-Time Scanning: Off"
(It was one of the top ten)
In step 3 of the solution (I think) There's a program you can download. Running this the first time didn't seem to do anything. I closed it and tried again this time just double clicking even though I have windows 7. This time it did something more but still didn't really seem to do anything.
Then I restarted my laptop and now it's fine so I'm not sure what resolved it. Probably that program.
Hope this helps