NtCreateKey stopped working

Our software uses NtCreateKey to create hidden (null) registry keys. It is out and working for years on thousands of computers with no problem.

Now, we have experienced, that on a single computer, it stopped working for a while and it returns access denied error (0xc0000022) for any attempt of opening any part of the registry. RegOpenkey works fine for the parent of the hidden key.

Has anyone experienced such a behavior?

Thank you