I tried to update git-annex via cabal. It fails due to lens not installing:

juh@sokrates:~$ cabal update
Downloading the latest package list from hackage.haskell.org
juh@sokrates:~$ cabal install git-annex
Resolving dependencies...
In order, the following will be installed:
lens-4.2 (new version)
DAV-0.6.2 (reinstall) changes: http-client- ->,
http-client-tls- added, http-types-0.8.4 -> 0.8.5, lens-4.1.2 ->     4.2,
network- added, optparse-applicative- added, xml-    conduit-
->, xml-hamlet- added
git-annex-5.20140707 (new package)
Warning: Note that reinstalls are always dangerous. Continuing anyway...
[1 of 1] Compiling Main             ( /tmp/lens-4.2-3107/lens-4.2/Setup.    lhs, /tmp/lens-4.2-3107/lens-4.2/dist/setup/Main.o )
Linking /tmp/lens-4.2-3107/lens-4.2/dist/setup/setup ...
Configuring lens-4.2...
Building lens-4.2...
Preprocessing library lens-4.2...

    Could not find module `Control.Monad.Trans.Except'
    Perhaps you meant
      Control.Monad.Trans.Cont (from transformers-
      Control.Monad.Trans.Error (from transformers-
      Control.Monad.Trans.List (from transformers-
    Use -v to see a list of the files searched for.
Failed to install lens-4.2
cabal: Error: some packages failed to install:
DAV-0.6.2 depends on lens-4.2 which failed to install.
git-annex-5.20140707 depends on lens-4.2 which failed to install.
lens-4.2 failed during the building phase. The exception was:
ExitFailure 1

I am not an experienced user of cabal. So any hints to solve the conflicts are appreciated.