[Haskell-cafe] difference "cabal configure" and "runghc Setup.lhs configure"

i have a strange error, which does not occur when i run runghc Setup.lhs configure but when i use cabal configure and then build, it occurs. the error is Type constructor Control.Exception.Exception used as a class in the instance declaration. (i have imported qualified Control.Exception) two questions: 1. Exception is a class (in Control.Exception) - why the error? 2. why is there a difference between runghc and cabal (using the same cabal file). i attach the cabal file and the two configuratin files produced.