Git push results in “Authentication Failed”

I have been using GitHub for a little while, and I have been fine with git add, git commit, and git push, so far without any problems. Suddenly I am having an error that says:

fatal: Authentication Failed

In the terminal I cloned a repository, worked on a file and then I used git add to add the file to the commit log and when I did git commit, it worked fine. Finally, git push asks for username and password. I put those in correctly and every time I do this, it says the same error.

What is the cause of this problem and how can I fix it?

The contents of .git/config are:

[core]
        repositoryformatversion = 0
        filemode = true
        bare = false
        logallrefupdates = true
[remote "origin"]
        url = http://www.github.com/######/Random-Python-Tests
        fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
        remote = origin
        merge = refs/heads/master
[user]
        name = #####
        email = ############