The "map" commands in grub4dos are sometimes tricky.
I don't know enough about grub4dos to suggest a specific solution, but
map --mem /ubcd/images/fdubcd.iso.gz (hd32)
map (hd32) (cd)
and similar codes are frequently presented with similar questions as in this topic, in sites about booting with grub4dos. Also frequently, the solution comes in the form of changing the "hd32" by some other option, more compatible with BIOSes. Something like (0xff) , or generally "(0xMN)" where MN might be "A0", "00" and others.
I'm sorry I can't be more specific (like for example about the exact meaning or the exact consequences about each MN pair of values).
Since we are talking about at least 2 images (fdubcd.iso and fdubcd.img), maybe more "map" and more "hook" commands are necessary.
About testing with SYSLINUX/ISOLINUX, are you already using v.4.06? If
it doesn't work as expected, maybe the new ifmemdsk.c32 syslinux module could be helpful? (I haven't used ifmemdsk.c32 yet, so I am not sure if it is actually useful to solve the current situation.)
I don't like being so vague, but I just thought that maybe thinking out loud may trigger some idea from someone else.