ghc 6.6.1: internal error: asyncRead# on threaded RTS

import Control.Monad (liftM)
import Data.Char (isAlpha, toLower)
import qualified Data.Map as M
import qualified Data.ByteString.Lazy.Char8 as B

main :: IO ()
main = do
  a <- B.map toLower `liftM` B.readFile "data_capitals"
  B.putStrLn a

:l try1
[1 of 1] Compiling Main             ( try1.hs, interpreted )
Ok, modules loaded: Main.
*Main> main

<interactive>: internal error: asyncRead# on threaded RTS
    (GHC version 6.6.1 for i386_unknown_mingw32)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.