I'm installing a 2x2GB 1066MHz kit into a mid 2010 macbook. When using both chips, I start up the computer a few times and I randomly get either the 1 beep or 3 beep error. I tried switching their positions as well. I then tried using just one of the new chips and had the same problem for each chip in each slot. Then I tried using one old chip (1GB) with a new one and it booted fine. I double checked in About this Mac and confirmed it was detecting 3GB. On top of that, the computer was way faster so I'm positive the new chip was being detected and used properly. Again I tried all possible configurations and it worked fine. Also tried resetting the PRAM/NVRAM with no luck (some people suggested it from things I've read). I've also seen that the symptoms I'm getting are caused by my new ram being too fast for the computer and only works when an older chip is used to slow it down. What's confusing is that both kits are the same speed and have the same timings (7). Any ideas?