Installation fails

[HJvT]

The installation fails with the following messages (dependencies are already installed);

C:>cabal install castle
Resolving dependencies...
Configuring castle-0.1.0.0...
realgcc.exe: ./specs: Permission denied
Failed to install castle-0.1.0.0
cabal: Error: some packages failed to install:
castle-0.1.0.0 failed during the configure step. The exception was:
ExitFailure 1

C:>cabal --version
cabal-install version 1.18.0.2
using version 1.18.0 of the Cabal library

C:>ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.6.3

OS: Windows XP