I had the same problem. Slingplayer for Facebook was for some reason the only way my laptop could see the video that was being sent out by my slingboxes. I know it worked 2 months ago last time I was overseas. Today I tried to use it and I got the errors. Really makes me mad because I use the slingbox to watch US sports while I am overseas.
What happened to the SlingPlayer on Facebook? It was the best way to watch my Slingbox, but all of a sudden, it stopped working.
All it says now is: "Sorry, something went wrong. Click Continue to try again." Then, when I click Continue, it goes to a 404 Page not found error on Facebook.
The "Slingplayer for Web" works half the time. It always launches the video on my main screen, but when I drag the window to the other monitor (extended desktop set up), the video on the Sling Player freezes half the time, and will require to reconnect and then it fails to reconnect most of the time. It's frustrating to say the least.
Not sure if there is a solution...