The generator matrix

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

generates a code of length 9 over Z2[X]/(X^2) who´s minimum homogenous weight is 6.

Homogenous weight enumerator: w(x)=1x^0+20x^6+64x^7+46x^8+40x^10+64x^11+16x^12+4x^14+1x^16

The gray image is a linear code over GF(2) with n=18, k=8 and d=6.
As d=6 is an upper bound for linear (18,8,2)-codes, this code is optimal over Z2[X]/(X^2) for dimension 8.
This code was found by Heurico 1.16 in 0.000836 seconds.