If you find that RunOnce & RunOnceEx Registry keys not being executed in Windows 10 or Windows 8/7/Vista then the reason could probably be that you are logged in as a Standard user.
A command set to execute via RunOnce or RunOnceEx may not execute as expected.
The registry keys affected are:
Standard Users do not have appropriate permissions to execute from HKEY_LOCAL_MACHINE.
Commands executed from the HKEY_CURRENT_USER RunOnce or RunOnceEx keys should work as expected, if logged in with an Admin account.
This is by design and to execute commands from HKEY_CURRENT_USER, you must log in with an Administrator account, says KB2021405.
This will therefore occur if you log on with a Standard User Account.
This issue affects only users with a Standard User account. If the user has an Administrator or Split Token, the execution proceeds.
Hope this clarifies things.