The timing for the Spartan-6 device is very tight and requires the use of area constraints in order to meet timing.
There are some constraints in the example design UCF to help meet timing, however in some cases the user will need to modify the area constraints to meet timing.
You can modify the constraints using the PlanAhead tool, or by editing the UCF file in a text editor.
You can also change the map options (-register_duplication, -logic_opt, -retiming), or apply an area group.
For a detailed list of LogiCORE IP Display Port Release Notes and Known Issues, see (Xilinx Answer 33258).