I build Haiku Once On Ubuntu and the next time it wont build.
- jam clean
then try building Haiku
If that still does not work then,
2) delete your generated folder, svn update your buildtools and haiku source, compile buildtools and try building haiku.
buildtools were updated recently and you will need to use the newer ones.
#1 above may work but better to do #2.
Also, giving an error message when building would give more helpful information to see what is going on.