Well, check out the documentation for the DCM/PLL inputs. It will mention what kind of inputs it does and does not like. It does not like regular boring inputs. It likes global clock nets. Which is why you need the ibufg. And you probably have the "Insert IO Buffer Thingies" option turned to OFF, or otherwise the tool would have inserted the IBUFG for you. Either way, try that line I gave you, that should solve the problem.
And no, not in that line with the module you post there. Where does sysclk come from? Is it an input from an external cmos oscillator? You want the IBUFG on the top level module, if this SysClk is coming from outside the fpga.