Synth 8-1031 "Varible" is not declared, when using "Varible" in an if statement

`timescale 1ns / 1ps

    module main(
        input clk,
        output Hsync,
        output Vsync,
        output reg [3:0] vgaGreen,
        output reg [3:0] vgaBlue,
        output reg [3:0] vgaRed,
        input Modechanger
        );
        //Declare some counters
        reg [23:0] clkCounter;
        reg [10:0] Hcounter;
        reg [10:0] Vcounter;
        localparam threshold = 2000000; //25MHz

        //Clock divider
        always @ (posedge (clk)) begin
            if (clkCounter == threshold -1)
                clkCounter <= 24'b0;
            else
                clkCounter <= clkCounter + 1;
        end

        //Check and set position
        always @ (posedge (clk)) begin
            if (Hcounter < 799)
                Hcounter <= Hcounter + 1;
            else begin
                Hcounter <= 0;
                if (Vcounter < 524) begin
                    Vcounter <= Vcounter + 1;
                end
                else begin
                    Vcounter <= 0;
                end
            end
        end

          //Draw when in this range
          assign Hsync = (Hcounter < 96) ? 0:1;
          assign Vsync = (Vcounter < 2) ? 0:1;

          //How to draw, and what to draw
          always @ (Hcounter or Vcounter)begin
                //if inside drawable zone
                if (Vcounter >34 && Vcounter < 516)
                begin
                    if (Hcounter > 143 && Hcounter < 785)
                    begin
                    //Mode 1: Draw a red cross hair line, and green 
background
                        if(ModeChanger) begin
                            if (Hcounter == 464 || Vcounter == 275) 
begin
                                vgaGreen = 4'b0000;
                                vgaRed = 4'b1111;
                                vgaBlue = 4'b0000;
                            end
                            else begin
                                vgaGreen = 4'b1111;
                                vgaRed = 4'b0000;
                                vgaBlue = 4'b0000;
                            end
                        end
                        //Mode 2: green screen

                        else
                            vgaGreen = 4'b1111;
                            vgaRed = 4'b0000;
                            vgaBlue = 4'b0000;
                        end
                    end

                    else begin
                        vgaGreen = 4'b0000;
                        vgaRed = 4'b0000;
                        vgaBlue = 4'b0000;
                    end
        end
    endmodule

I'm trying to draw something to my screen using my FPGA board, this is 
the code I come up with, I'm new to Verilog and I don't really know why 
I get the error message "Synth 8-1031 ModeChanger is not declared". 
ModeChanger is a switch on my FPGA board.<br>
My first question is what cause the error?<br>
And my second question is will my code work as I expect? (ModeChanger 
on, draw a cross hair line, otherwise a green screen)<br>The reason I 
ask this question is because I don't have a VGA cable to test it 
out.<br>Please help me, thank you so much