Design Compilers's Illegal reference error

Hello,
I am running Design Compiler for synthesis the following code, but I have encountered this error
Error: m4k.v:58: invalid symbol single_onehot found in activation expression. (VER-254)
Error: m4k.v:58: Illegal reference to memory single_onehot. (VER-253)
reg [63:0] onehot;
wire [63:0] single_onehot [31:0];
reg [63:0] var_onehot;
integer k;
integer m;
always @(single_onehot) // Error this lines
begin: a1
var_onehot = single_onehot[0][NUM_WORDS - 1:0];
for (k = 0; k <= NUM_M4KS_WIDTH - 1; k = k + 1)
for (m = 0; m <= NUM_WORDS - 1; m = m + 1)
var_onehot[m] = var_onehot[m] & single_onehot[k][m];
onehot <= var_onehot;
end
Pls help me how to solve this. Thanks