What device are you streaming with? Generally, when I see that sort of issue, it is due to an anti-virus on the device (for example, Norton 360) preventing the stream from going through. You should be able to go into the anti-virus and add the SlingPlayer for Web plugin or SlingPlayer Desktop application to the allowed programs, and this should fix the issue. This is different on every anti-virus though, so I am afraid I couldn't tell you exactly where to make that change.
- Some Internet security and personal firewall software may interfere with your Slingbox setup or SlingPlayer
I hope this helps!!