Xst:528 - Multi-source error while synthesising using ISE

ERROR:Xst:528 - Multi-source in Unit <sin_wave2> on signal <i<3>>
ERROR:Xst:528 - Multi-source in Unit <sin_wave2> on signal <i<2>>
ERROR:Xst:528 - Multi-source in Unit <sin_wave2> on signal <i<1>>
ERROR:Xst:528 - Multi-source in Unit <sin_wave2> on signal <i<0>>

this is my code:

module sin_waveq (clk,rst,I,sine1);
input I,clk,rst;
output [7:0] sine1;
reg [7:0] index;
wire [7:0] value;
reg [7:0] sine1;
reg [1:0] i;
wire clk_4;
wire clk1;
reg en;
initial
begin
i=2'bZZ;
index=8'hzz;

end
assign clk1= clk;
always@(posedge clk)
begin
if (rst==1'b1)
begin
index=8'hzz;
en=0;
end
else
begin
index=8'Hff;

if(I==0)
i=2'b10;
else if (I==1'b1)
i=2'b00;
end
en=1'b1;
end

clock_4 clk123 (en,clk_4);

always @ (posedge clk_4)
begin
case (i)
2'b00 :begin index = index +8'd1;sine1=value;if (index ==8'd124) i= 2'b01; end
2'b01 : begin index = index -8'd1;sine1=value;if (index == 8'd0 ) i= 2'b00;end
2'b10 :begin index = index +8'd1;sine1=-value;if (index ==8'd124) i= 2'b11;end
2'b11 : begin index = index -8'd1;sine1=-value;if (index == 8'd0) i= 2'b10;end
//default :begin sine2=8'bzzzzzzzz; index1=@Q 8'b0; end
endcase
end

luk_sin2 aaa2 (index,value);

endmodule

Remove your "initial" block and move the "i" assignment to the reset if block where you already reset "index".

always@(posedge clk)begin // This is instances- 1
if (rst==1'b1)
begin
index=8'hzz;
en=0;
end
else
begin
index=8'Hff;

if(I==0)
i=2'b10;
else if (I==1'b1)
i=2'b00;end
en=1'b1;
end

always @ (posedge clk_4)begin // This is instances- 2
case (i)
2'b00 :begin index = index +8'd1;sine1=value;if (index ==8'd124) i= 2'b01; end
2'b01 : begin index = index -8'd1;sine1=value;if (index == 8'd0 ) i= 2'b00;end
2'b10 :begin index = index +8'd1;sine1=-value;if (index ==8'd124) i= 2'b11;end
2'b11 : begin index = index -8'd1;sine1=-value;if (index == 8'd0) i= 2'b10;end
//default :begin sine2=8'bzzzzzzzz; index1=@Q 8'b0; end
endcase
end


If possible try to bring all "i" assignments into single instances you can resolve the error

Please post in proper category of forum for good response

Missed that in the formatting of the code. Sudarsan is certainly right.