I had the same issue on window 8 64 bit machine, with this message in event log
Disabling AP was giving me this error in event log and with AP enabled I couldnt start ODS or Full Scan and was having a POPup window saying "scan64.exe failed to start".
Event ID: 512
Description: Process **\MCSHIELD.EXE pid (xxxx) contained unsigned or corrupted code and was blocked from performing a privileged operation with a McAfee driver.
Disabling Hooking rule in AP, worked for me first.
After this I identified that process which was trying to hook with McAfee's, it was quit suspecios application and I removed it, now it is all set with me.