The following code works for on GroupWise 6.01 and Formativ 1.5:
Sub Main(Client, GWEvent)
Because you are removing a menu item from the main GroupWise toolbar, the removal does not take place until the next time you start GroupWise. This is due to the design of GroupWise. Try restarting your client and try again.
If you continue to experience a problem, please advise the versions of GroupWise and Formativ you are using.