Mux4Way16 - What am i doing wrong? [Solved]

[e4c6]

My chip design for Mux4Way16 is as follows:

CHIP Mux4Way16 {
    IN a[16], b[16], c[16], d[16], sel[2];
    OUT out[16];

    PARTS:
    Removed
}

I'm not certain why i'm failing the tests. I thought Mux16(Mux16(a,b, sel0), Mux16(c,d, sel0), sel1) should suffice but obviously its not working as my test is failing. Can anyone point me at the right direction?

Edit: My Mux16 was wrong, sorry.