First check the voltage at the optos. I had some that tested fine on the switch tests, but the voltage change between blocked and open was not as significant as it should have been. Replacing them helped considerably. If you still have random opto problems I would consider buying the upgraded 16 opto board with the diagnostic lights. They have great tech support and were able to talk me through fixing a few things that weren't obvious. I had one that was showing partially good on the board diagnostics and the "sister" switch was actually the problem, not the one that was indicated. Turns out on the board they are wired in pairs. It took me a couple of months to figure out the problems, but mine has been running 100% since then.