Moving to Fedora Core 5 requires to rebuild all arch specific Fedora Extras packages. Accordingly build dates, this does not seem to have happened for this package. Please rebuild the package as soon as possible. When you did this already, ignore and close this bugreport please. For more information see http://www.fedoraproject.org/wiki/Extras/FC5Status.
Thanks for filing this. I'll probably update darcs to its latest release soon even though ghc hasn't been rebuilt yet.
ghc was rebuilt and darcs updated to 1.0.6.