Why the messagebox anyway if it's a scheduled task?
>> I am trying to make a backup job so the script must be placed in Scheduled Tasks. The messagebox is used for the admin to confirm if go the backup log folder for checking.

And how are you going to schedule the task to run under another user's account? Do you know the account passwords for your users?
>> There may be other admin to run that script. They may use other account to run that backup script e.g. bkupadmin and there are domain adminstator logon console. Then, the messagebox will be suspended on Task Manager. That's why I need to setup some condition to avoid a abnormal operation.

Scripts executed via scheduled tasks should not require user interaction
>> Thanks for your advice. I just want to make a user-friendly interface for administration.

There are UDFs that retrieve the interactively logged in user. that user will need to be identical to @USERID for your test to work.
>> Sorry, what's that mean?

Thanks