Hi
I had back then a weird problems with AC3D and AH materials. They seem to some how corrupt sometimes.
Did you check the .ac file material assignments with text editor? There should be a 'mat ' with number per object face:
(snip)
numsurf 28
SURF 0x30
mat 19
refs 4
0 0.010041 -0.089157
1 1.384997 -0.091469
2 1.372921 0.266267
3 0.020636 -0.014646
SURF 0x30
mat 19
refs 3
4 -0.175042 -0.393024
5 0.000000 -0.000000
6 -0.438140 -0.000000
(snip)
Check out the AH material predefinition list (256 lines) is at the beginning of the .ac file, between the 'AC3Db' and 'OBJECT world' lines.
Also you could send a sample file to me. Check your PM.