It worked before... for a while. And now it's borken (again) I don't understand why. Nearly everytime there's a new version of git comes out SourceTree authentication breaks. I tried switching to the embeded version of git and that doesn't work either.
I'm sorry to hear that Sourcetree is not working for you. Can you give us some more information about your environment to help us troubleshoot your issue?:
Let us know!