5019 - Invalid data passed to UrlDecode() function.

This error is generated when a browser parse form data containing the percentage (%) character to WBSP engine. E.g. if the browser mistakenly called WBSP file with the following
http://www.domain.com/somefile.wbsp?WB_BaseName=base.mdb&WB_Query=100% free&...
If you use form for sending data to WBSP file your browser and WBSP engine will take care of transferring the data.