[Haskell-cafe] what does the hidden package error mean?

I am trying to build ParseP on the latest ghc, and i am getting this error: Text/ParserCombinators/ParseP/Interface.hs:26:17: Could not find module `Data.ByteString.Char8': it is a member of package bytestring-0.9.1.4, which is hidden what does "hidden" mean? why does this work in ghci

import Data.ByteString import Data.ByteString.Char8

without any problems