Try doing a factory reset of your Slingbox Pro. (http://us.slingmedia.com/get/KB-005036.html)
If that doesn't help, it could be a heat issue. Try moving the Slingbox into a better ventilated area. I personally had heat issues when I had my Slingbox ontop of my DVR inside an entertainement system. After moving the Slingbox and the DVR outside of the cabinet helped reduce my issues. In fact, once I moved it away from the DVR, I rarely if ever have any issues.