I was having problem while trying to clone the gitosis-admin repository from the server. Every thing was setup as per the instructions, but it will never get cloned on to my windows client "GIT extensions". It was exiting with an "Access Denied" message. To my surprise it was working perfectly on my Linux and other machines.
After some head banging, I found that the host name that I was using to connect the repository was already saved as a profile in my putty and was having a different private key assigned to it than the one I should use for gitosis. So I renamed the profile and guess what, it worked like a charm !!!.