I have GHC/Haskell-Platform installed into a directory that is not typically in my PATH environment variable. When I was setting up EclipseFP I could point the preferences at my GHC location and my Cabal location without problems. However, when trying to build Scion it fails by telling me that "cabal: ghc version >=6.4 is required but it could not be found."
I looked at the source and it looks like net.sf.eclipsefp.haskell.ui.internal.scion.ScionBuilder assumes that GHC will already be on the path, rather than passing in the --with-compiler option to cabal when installing Scion.
It would be a nice improvement if EclipseFP would use the version of GHC that I configured it with when trying to build Scion.