Franz,
First off, the sources for this recipe should be included on the source ISO. It's possible the local sources where deleted by a 'bitbake -c cleanall virtual/linux' perhaps and now it's trying to access our internal git repositories. You can try extracting the source again from the ISO and it should pick up the local sources. An option to keep this from occurring again is to change the permissions on the files in the sources directory.
If you don't want to do that, switching to the external git for that recipe should work too. Can you post a diff of what you changed for the Linux recipe so I can look at it? Note: This won't work for all recipes, since some of them are ONLY available from the ISO and don't have a public facing git repository.
-M