Try 1
Try 2
Try 3
If your Sourcetree version is < 3.0 (like it was in my case), download the latest stable version from sourcetreeapp.com.
NOTE:
Even though the downloaded file's name is "SourceTreeSetup-#.#.#.exe", just executing it will install/replace any shortcuts you might have created
As of the time of writing, upon download and executing the downloaded file, (v3.4.3, as shown above), the Repository Settings now has some additional settings, for Host Type Unknown, as shown below:
Try pushing changes again...