It's very odd that the Slingbox is working properly on a PC but not in a Mac. I recommend checking if your Mac and the browser meet the minimum requirements. It's important to confirm if your Mac has an Intel or a PowerPC; check this out:
You also might want to have a look at the following links:
I have two Macs and they both have the same issue. Occasionally, they can connect but certainly not reliably. Both Macs meet the minimum requirements & they are 1 and 2 years old. This only started after the last Slingplayer update was installed. I have since bought a dedicated PC for our the main TV & Slingbox works on that everytime. Still very limited success on the Macs. The Slingbox is still under tech support but the tech was unable to help since the Slingbox unit is located in a different country. They suggested it is set-up incorrectly which I doubt. They worked just fine until the update. Pretty disappointing considering everything had been working fine.
I agree I am having the same Mac issues watching on my computer within my LAN. The software setup module just cant connect to my slingbox yet I can connect to it over the internet from my computer. I go to the set up screen on the web and it sees I am logged in. Yet the siling box window "initalizing" forevver then crashes my browser.