If you find that RunOnce & RunOnceEx not being executed in Windows 7 or 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 effected 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.
To execute commands from HKEY_CURRENT_USER, you must log in with an Administrator account.
KB2021405 states that this is by design and to execute commands from those registry keys, you must log in with an Administrator account.
This will therefore occur if you log on with a Standard User Account.
This issue effects only users with a Standard User account. If the user has an Administrator or Split Token, the execution proceeds.
Description of the RunOnceEx Registry Key may also interest you!