Description
You may see this warning in the Quartus® II software version 12.1 for designs that use the Altera_PLL megafunction. The cascade_out port is used when cascading one fPLL to another adjacent fPLL. If you do not enable this port in the Altera_PLL megafunction in your design, the warning may still be generated during compilation.
Resolution
You can safely ignore this warning. It is generated by mistake.