Beginner's doubt -404 error-- File not part of project!

[Vic Hood]

Hi folks,
I have two instances of a program that im developing in my IDE(Eclipse Galileo).Both of them are opened as two different projects , I plan to use one for development and the other one to show the last obtained output when asked by the lead/management .But now, when i tried to run my backup project , it fails saying resource not found ,and the associated file(the supposed missing resource) is in the project I used in developement and not the backup . I double checked the web.xml , restarted eclipse, yet the same error . Any clues on how I could solve this?