You can delete the profile database (VoiceAttack.dat) at
%Appdata%\VoiceAttack
(you can press Win+R, paste that into the "Open:" field, and click OK to go straight to that folder)
To completely get rid of everything, delete the "Backup" folder as well.
If you have profiles you want to keep, you could also hold the shift and control keys while VoiceAttack starts to bring up the "VoiceAttack Load Options" dialog, and check the "Disable profile initialization commands (this session only)" option which will stop the profile from running its startup command so it won't try to invoke the plugin