The last time I came across this issue, I found that the Mac had some antivirus installed that was interfering with the app in some way. If that's the case in your computer, I would recommend temporarily disabling the antivirus entirely, and try re-launching the app. Here is an article to take a look at:
If un-installing and re-installing doesn't work, try rebooting some things, such as your computer and your router.
Hope this helps!
Just experience the same issue on windows 8.1.
Slingplayer Desktop suddenly started to hang on the initialization screen, even though it worked perfectly fine early in the same day.
Fixed it by adding exceptions to windows defender. Created exceptions for the slingplayer process as well as the directory.