Are you running Windows Vista x64? If so, give this a try, report back either way.
You'll need to open an elevated command prompt (Command Prompt in the start menu and then "Run as Administrator")
Once you have that opened, copy this line in there:
bcdedit /set loadoptions DDISABLE_INTEGRITY_CHECKS
Then restart the computer when that's done. Remember, report back.
EDIT: Might have only worked for beta. If it doesn't work, then use this line to restore the way it was:
bcdedit -deletevalue loadoptions