How to disable driver signature enforcement mode if bcdedit /set TESTSIGNING ON fails?

I have been trying to set up some experimental driver, but I have typed quite several times:

bcdedit /set loadoptions DDISABLE_INTEGRITY_CHECKS
bcdedit /set TESTSIGNING ON

Now I have an error saying:

C:\WINDOWS\system32>bcdedit /set TESTSIGNING OFF
An error has occurred setting the element data.
Access is denied.

I am typing in Administrator prompt.

What should I do to make it work and boot in test mode once again?

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.