Have you tried a different web browser? If you were using Safari you can install Firefox to determine if the issue persists. Also you can try to reset the browser settings, you can find the instruction at this link from Mac support,
Second problem is that I simply cannot watch the slingbox form over the internet. It worked great with the player (I shouldn't have thrown it out!). But now, no way. And I have my ports set up correctly.
Just try to run the Internet Viewing setup manually at the Slingbox location and that should fix this trouble to connect remotely to the Slingbox.
Let us know if that works. Kind regards