Error (12014): Net "key_Qk_shift_i[5]", which fans out to "mod16:generate_block_identifier[4].f1|x[1]", cannot be assigned more than one value

genvar i,j;

generate

for (i=0; i<=25; i=i+4) begin : generate_block_identifier // <-- example block name

mod16 f1 ( key_Qk_shift_i[i+3:i], new_salt_Or[i+3:i], input_data[i+3:i], r_out[i+3:i], xor_out[i+3:i], clk ,CurrentState);

for (j=0; j<=25; j=j+4) begin : generate_block_identifier_2

shift_mod shift ( key_Qk, CLK, currentState, j, key_Qk_shift_o);

end

end

endgenerate

key_Qk_shift_o is the output of the module

and key_Qk_shift_i is the input of the other module

this is how i am connecting them

wire [255:0] key_Qk_shift_i;

wire [255:0] key_Qk_shift_o;

tri [255:0] key_Qk_shift;

assign key_Qk_shift = key_Qk_shift_o;

assign key_Qk_shift_i = key_Qk_shift;

any help plz