[Haskell-cafe] Cabal install problem

[Victor Miller]

Lately whenever I try to install a cabal package it fails with the
following error message:

Could not find module `Control.Monad.State':
     Perhaps you haven't installed the profiling libraries for
package `mtl-2.0.1.0'?
     Use -v to see a list of the files searched for.


The strange thing is that I can load Control.Monad.State from ghci.
How do I fix this -- i.e. where should I look?