Take a look at the following links. You'll find the most common reasons for this behavior.
I have been streaming a Slingbox Pro HD from Seattle to Amsterdam on a regular basis for 11 months now. I have had many problems with the picture and sound freezing. It would freeze for about 8-10 seconds, every 10 minuets (or every 10 seconds some days), then start streaming again. It would stream at about 1500 kbps and work fine, then crash down to 0 and freeze. I have tried to resolve this with Sling support, the Seattle end, and Amsterdam, but nothing has worked. Until now. I started using Firefox (only for the Slingbox) instead of Internet Explorer about a week ago, and have not had one freeze up since. It now runs consistently at about 2800 kbps. I don’t know why this worked, and frankly I don’t care. All I know is that my Slingbox has been working flawlessly streaming from Seattle to Amsterdam for a week now, with no issues. I hope this helps somebody, because I know how happy it made me when I realized it was fixed.