Oh man, I have the exact same problem!! This just happened to me a couple weeks ago. It was all working fine..ps3 games in 3D, 3D blu rays, xfinity 3D channels...then poof. I get the same "mode not supported" from the ps3 and nothing but passthrough from cable. The Mitsubishi box never flips to 3D mode.
I tried to get help from tru3d and got one response from the President of the company....asking for my order number. Then they went radio silent and haven't replied since.
I tried swapping out the mitsu box with a new one but that didn't help. So either it's as someone posted above...they tweaked the adapter, or the Gefen has been messed up...I dunno.
Keep me posted and I'll do the same. I know your pain!!