I tried changing a few instances to Data.ByteString.Char8 without success. The error that I receive involves dependencies that are in Prelude not being found. You can also reproduce this error in `cabal repl` fairly easily:

https://gist.github.com/jsl/7294493

Perhaps it could help to homogenize the serialization of the interface file in `Setup.hs` to be consistent with the way that we're reading the file?