If you have used Web Prospect to download mail from an existing account and ended up with hundreds of emails that you want to purge (not process), there is a simple way to do this outside of the program.
The email that is downloaded for processing is kept in this folder: %APPDATA% then "\Roaming\Northwoods Software\WP\Registrations." If you remove the items from that directory, that will clear the queue in Web Prospect. It would be best to have Web Prospect closed when you do this, and when you reopen it, the Main tab should not have any emails showing for processing.