Repair Permissions
After you have identified and fixed the underlying cause (see below), you'll want to repair the permissions:
cd /path/to/repo.git
sudo chgrp -R groupname .
sudo chmod -R g+rwX .
find . -type d -exec chmod g+s '{}' +
Note if you want everyone to be able to modify the repository, you don't need the
chgrp and you will want to change the chmod to sudo chmod -R a+rwX .
