for that cpu, it can only work in a single cpu configuration.
For a cpu your wanting, you'll need to look for one that has 2 QPI links or it says "Max CPU Configuration 2"
For example like thishttp://ark.intel.com/Product.aspx?id=47925
Another easy way to identify cpu's for dual and single configurations by there name (unless intel change something that i dont know of)
W= Single cpu configuration (workstation)
E= Dual configuration
L= Dual configuration (low power cpu's)
X= high end dual configuration.
So for example the W
3565 cpu can only be in a single cpu configuration.
Hope this helps and welcome to Tom's hardware forums!