Invalid Signal Splitter Error

Hi everybody!!

I am using a CycloneIII mounted on an evaluation board, and I have to use the ddr2 memory mounted on it. I control the memory operation with the HPCII controller. To use all ddr2 memory devices on the evb (4 MT47H32M16CC-3 and 1 MT47H32M8BP-3) I have to duplicate the control signal, but when I try to do so, the "invalid Signal Splitter" error comes out.

I try to duplicate in this way:

wire ddr2_a; //output from the ddr2 controller

assign ddr2bot_a = ddr2_a;

assign ddr2top_a = ddr2_a;

Someone has advices?

thanks