Please follow the below steps to re-enable the real time scanner :
Ø Check and delete if you have any other security software installed in control panel and their files folders in C:/program files & common files.
Ø Click Start, Run, type services.msc, and click OK.
NOTE: Windows Vista and 7 users should click the Windows Orb, type services.msc in the search box, right-click services.msc, select Run As Administrator, then click Continue.
Ø Locate the McShield service and check the status. If the status is Stopped, right-click the McShield service and click Start.
Ø When the status shows Started, close the Services window.
ØOpen McAfee Security Center and verify that Real-Time Scanning is enabled.
Ø Restart the computer and verify that Real-Time Scanning remains enabled.
After reboot, Real Scan still needs to be turned on but doesn't go off every 7 seconds. I followed your suggestion, McShield shows as "Started". I still have to turn on Real Scan after start. I am also getting "Some components of ActiveShield are either missing or might not have been installed properly. Please reinistall ActiveShield." I looked on the McAfee website but cannot find reinstallation info. Do you know where it is? Thanks!
The error : Some components of ActiveShield are missing can be caused due to several reasons like,
Any other other anti-virus programs are installed
Any older version of mcafee programs existingin the computer.
Please check whether there exists any other security software in control panel or its remnants in C:/program files or common files and delete of found.
The steps to uninstall mcafee using the removal tool and to reinstall is explained in this document
Do report back if you need any further assistance on this.