The generator matrix

 1  0  1  X  1  1  1  1  1  1  1  1
 0  1  X  1 X+1  1  0  X X+1  1  0  X

generates a code of length 12 over Z2[X]/(X^2) who´s minimum homogenous weight is 12.

Homogenous weight enumerator: w(x)=1x^0+13x^12+1x^16+1x^20

The gray image is a linear code over GF(2) with n=24, k=4 and d=12.
As d=12 is an upper bound for linear (24,4,2)-codes, this code is optimal over Z2[X]/(X^2) for dimension 4.
This code was found by Heurico 1.16 in 0.000231 seconds.