Hi!
We suspect that it's application's default page was not found - not the RedirectToApp.aspx itself. If so, then the most likely cause is that the application was registered with incorrect physical folder, and/or incorrect default page. Launch Cassini Explorer from (Programs | Ultidev | Cassini Web Server | Cassini Explorer) and try to launch the application from there. Eventually you may have to re-register your application with exact full folder path and default page file name.
If it's RedirectToApp.aspx is not found, then Cassini service may have been stopped. Please run Programs | Ultidev | Cassini Web Server | Restart Cassini 2.0 Service to start the service.
Please let us know if you need any further help.
Thank you for usign UltiDev Cassini,
UltiDev Team.
Please donate at
http://www.ultidev.com/products/Donate.aspx to help us improve our products.