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Code:
{vb:raw template_hook.showthread_adminoptions}
That's the hook that needs to be in your SHOWTHREAD template for the "Administrative" menu option to work.
It was added in VB 4.1.8 but if you have a custom style it's possible the style author did not include it if they were basing off an old version.
If the search does not find that code in SHOWTHREAD template then follow the instructions for edit #3.