What's happened? Why has your proposal fallen apart? Sounds like you should get together with your supervisors and talk about how it can be modified/improved. PhD's are full of highs and lows, like VHB said, don't give up! :o)
Don't sweat it out! Who said your proposal was unsuitable and why? It happened to me as I was told my proposal was suitable 1 week before the interview and told to come up with an alternate one! I've never read so much in such a short space of time or written as fast so it can be done! Good Luck!