I had a similar problem when I first installed my Slingbox. I could see it fine when using a computer attached via Ethernet or Wifi to the same router that my Slingbox was connected to via Ethernet. But could not find the Slingbox from any location outside the local area network of the router.
My problems all went away when I programmed the router to assign a static IP address to the Slingbox, then programmed my router to forward port 5001 with "both" protocols (TCP and UDP) to that static IP address assigned to the Slingbox.
Rebooting both the router and the Slingbox once made everything work great, and it has worked great without a hitch for the several months since.
Well, I got it to work. This is what I finally did. I went back to SlingPlayer 220.127.116.115. I had to go out on the Internet and found it on some legacy site.
After spending I don't know how many hours using the web version and then SlingPlayer 2.xx I just gave up. I uninstalled both and rebooted the computer. Then I downloaded version.1.5.xxx, installed it. Reset the Slingbox and away we went. Slick as can be. Now every computer in my house can access my slingbox.
It doesn't get any better than that.
I don't think it had anything to do with that notice when I logged on today about a bad update to the PRO HD because mine is just a PRO and I didn't do any updating.
Hope this helps someone else.