Cabal says parsec-3.1.1 not available, ghc-pkg says it is available

[Henning Thielemann]

I am lost. Cabal-install says 'there is no available version of parsec that 
satisfies ==3.1.1', but ghc-pkg says I have this parsec version installed.

mypkg$ cabal install --constraint=parsec==3.1.1
Resolving dependencies...
cabal: There is no available version of parsec that satisfies ==3.1.1
mypkg$ ghc-pkg list parsec
/usr/local/lib/ghc-7.0.1/package.conf.d
/home/bla/.ghc/i386-linux-7.0.1/package.conf.d
    parsec-2.1.0.1
    parsec-3.1.1
mypkg$ cabal --version
cabal-install version 0.8.2
using version 1.8.0.6 of the Cabal library


Maybe parsec is somehow installed incompletely?
'ghc-pkg check' shows no error.