I am having the same problem, but I have done some research. If you look at the manual or online (http://www.intel.com/support/motherboards/desktop/dp45sg/sb/CS-029151.htm) it shows the supported DIMM configurations as well as the tested memory. It looks like the board only supports 1gb at 1333mhz per memory slot. So if you are using a 2gb memory stick then the motherboard only supports 1066mhz 2gb memory per slot. That is why the motherboard fails when you try to change in the bios to 1333mhz. If that wasnt enough the cas latency for 1333mhz only supports 9/9/9 or 9/10/10. Which sucks because I have also purchased Ballistix memory that has a cas of 6/6/6 and is pretty much useless because the motherboard is going to only read it as 9/9/9!