Thirty-something feet doesn't exceed the HDMI spec, but it's creeping close to it. You might get Outlaw's take on it, but that's the most likely source of the trouble.

Switches can produce HDCP problems, and some displays and source components get finicky when there's a switch in the signal path. The switching provided by Outlaw's gear has not seen much of this. I think you've pretty well ruled this one out, though, because 720p works and HDCP doesn't differentiate between resolutions.