both games are beta, have you tried running on a released game ?
try running it on a single 580gtx.
when you say latest drivers are they the bf3 beta ones ?
when the error comes up does it detail any more information ?
this is what normally happened when you have overclocked too much or your cards are running too hot possibily, have you tried something like occt to check that your system is stable with their current clock speeds?
And yeah i have tried both in the same PCI-E slot
sounds like the one gfx card is having problems then.
download gpu-z and check the temps of the cards.
Nvidia & ATI have just released a new set of drivers for their video cards specifically built for Battlefield 3.
http://battlefieldo.com/nvidia-ati-bf3-drivers-released/
Try Nvidia GeForce 285.38 Drivers.
Nvidia GeForce 285.38 Drivers Release Notes
•Increases performance in Battlefield 3 by up to 38 percent.
•Improves overall stability and image quality in Battlefield 3.
•Adds or updates SLI profiles for Battlefield 3.
And to do a temp test is not needed as you can feel the diffrence it gets that hot lol.