Regarding megafunction cycloneii_crcblock

I am trying to access the CycloneII_crc block using the megafunction (cycloneii_crcblock). I have appended my code with this message. The code compiles and synthesize and maps properly. However, when I try to run the timing simulations the output of the crc-block CRC_ERROR, REGOUT, always remain at undefined state. I tried several combinations of shiftnld and ldsrc. I suplied 50MHZ clock in the waveform, I ran the simulation for up to 50ms (which takes about 5mins to run)

Any help will be appreciated.

Thank you in advance.

============my code=================================

module light(a, f, y, x1, x2,CLOCK_50, e, z,);

input a, x1, x2;

input CLOCK_50;

output f, y, z;

output e;

assign f=(x1&~x2)|(~x1&x2);

assign y= ~z;

cycloneii_crcblock XOR_research

(

.clk(CLOCK_50),

.shiftnld(a),

.ldsrc(f),

.crcerror(e),

.regout(z)

);

endmodule