System.Linq name space not recognized/resolving

I copied a solution to another development machine, open in visual studio 2008 and it starts to throw name space/missing assembly error for System.Linq. But when I look around in adding the reference I can’t find a System.Linq anywhere. What was wrong?
After some digging around I found the solution to this is to add System.Core to your reference. The Linq name space needs that to work.
Summary, to fix missing assembly error for System.Linq, make sure to add reference to System.Core.