It sounds like you have file in the git repo owned by root. Since you're ssh'ing in as 'username' to do the push, the files must be writable by username. The easiest thing is probably to create the repo as the user, and use the same user to do your pushes. Another option is to create a group, make everything writable by the group, and make your user a member of that group.
~ Answered on 2012-10-30 20:48:44