The command line seems fine. As the crash happens after the mining has started perhaps the overclocking settings of the cards are too high. In the first few minutes the miner will perform auto-tune as there is not explicitly specified -gt parameter. You can try the following things to fix the problem:
  * Start the miner only with half GPUs (add -gpus 123456 to start with 6 GPUs only) and see if it still crashes. If not, wait until auto-tuning is over (it usually takes less than 5 minutes), press 's' on the miner console window and write down the -gt values (they should be fairly similar if the GPUs are the same). Then try to start the miner again with all GPUs but with added -gt parameter (e.g. -gt 45 if the best found -gt parameter was in 43-47 range for the individual GPUs).
  * Lower the memory clocks and/or increase the core voltage sligthly.
  * Try using the non-green kernels (remove -clgreen 1) or try using the alternative kernels (-clkernel 2)


   Thank you for reporting about the problem with the 'c' key. The message about switching to dual-mining mode is harmless but we fixed than anyway in 4.0b.
   -proto 3 works as before for us. Can you please send us a command-line example where it doesn't work?


   Can you please send us the log for the first 1-2 minutes? We are unable to reproduce this problem here.