Error: Cannot find source node 'ddr2_dqs[0]_in' -- help me DDR2 in sopc

I received an error similar to this and it was a result of the first situation. For me, I was instantiating a tester around the interface, so I'd insert data and read back data. The problem with that is that Quartus will end up "optimizing" away some of your connections, not knowing that they are actually important. The way I got rid of the errors was to place output pins on each of the connections, thereby telling Quartus that the connections were important and not to "optimize" them away.