Description of problem: darcs.cgi uses errors.xml to look up error message text, but the file is not packaged by the RPM. Version-Release number of selected component (if applicable): darcs-server-1.0.9-6.fc8
bug filed and fix applied upstream. I'm going to wait a bit and see if another upstream stable release happens soon, and it includes this fix.
Fixed in 1.0.9-10.fc9.