AMS simulation test failed

I am getting the error below when I try to netlist and run AMS simulation. I am not sure what the problem is. Please help if somebody know how to fix this error.

*Error* index:argument #1 should be a string (type template = "tS") - nil

In this schematic, there are three same pulse signal suppliers, two exactly same verilog blocks, and one OR-gate which is used from ahdlLib.

Logic of two verilog blocks: 

module half_adder(a, ,b, s, c);

input a;

input b;

output s;

output c;

assign s=a^b;

assign c=a&b;

endmodule

config details are showing below. Please take look if it is helpful.

I'd appreciate any suggestions for fixing this error. 

Thank you very much,

Chofield.