Good morning,
In Windows 2003 server, outlooks will give you a confirmation window if you try to send an e-mail from outside outlook.  ("This program is trying to send an e-mail on your behalf.  Do you wish to allow it?").  This makes it so sending programmatically from a .vbs is not allowed normally.  There are a few programs out there that you can buy to sit on the desktop, where you can specify a set of programs that are allowed to send e-mails for you without confirmation.  
When we execute an Execute Script task, what is the name of the .exe that is trying to send the e-mail?  I've tried wscript, cscript, and even the VisualCron_Server.exe, but none of those worked. 
Regards,
Alan.