Thank you for the information provided. I see you're having trouble getting your Slingbox to work properly with your updated MAC OS Computer. We've been able to identify a problem with customers having problems once they have update there apple device. Our engineering is working on a fix right now. The fix will require an update to the app. We the forum community, will keep you posted as soon as we submit the updated app to the app store.
Although, Slingbox customers have successfully accessed watch.Slingbox.com through a different browser such as Chrome, Internet Explorer or Firefox.
Sling Media Support