This question is related to my problem in understanding rebase, branch and merge, and to the problem
How can you commit to your github account as you
One possibility that the above answers don't address is that you may not have an ssh access from your shell. That is, you may be in a network (some college networks do this) where ssh service is blocked.In that case you will not only be able to get github services but also any other ssh services. You can test if this is the problem by trying to use any other ssh service.This was the case with me.