I had two GTX 560’s in linux for 1.5 years until a month ago. In my experience, SLI in linux is less than worthless. Always has been. You can waste countless hours messing with it (I did) and it never works (by “works” I mean using two cards in SLI mode resulting in better performance than a single card). I ALWAYS HAD BETTER PERFORMANCE WITH REMOVING THE SECOND CARD FROM THE SLOT AND ONLY USING ONE CARD. Not yelling at you… just using capitalization for emphasis here. I NEVER found a single instance in linux where the second card in SLI didn’t DECREASE performance noticably. In my opinion, you’d be better off removing the second card, or at least removing the SLI bridge and using a single card. That’s just the cruel reality of nVidia’s linux driver.
I wish you luck… but I’ve already chased my tail for way, way too long trying to get SLI working. Didn’t like the fact that I paid for 2 cards and got less performance than I could have gotten with just one :( If you don’t dual-boot with Windows, you’re better off selling the second card. If you remove the second card and your red screen goes away, that is the best your two cards will perform in linux (leaving one in the box you bought it in “fixes” SLI.
Or do what I did… keep thinking the situation if “fixable”… scour every forum, try every command line switch or setting, environmental variables… all the while your second card is decreasing in value and could have been sold while it still had value.