What files do you find inside ".d1x-rebirth"?
Maybe you just copied "d1x-rebirth" and renamed it to ".d1x-rebirth"?
What should be found inside is:
descent.cfg
player.plx
You can also check what res is set inside descent.cfg
Another possibility is we have a little misunderstanding here.
When you mount the SD card on your pc, the path is /local/home, however when run on dingux, the path is /usr/local/home, because dingux mounts the sd card to /usr/ dir.
If you happened to copy the files via telnet on a running dingux, /usr/local/home is the right dir to put /d1x-rebirth dir in.
YET ANOTHER possibility is that you don't have the HOME variable set properly.
How does your /local/sbin/main file look like? It should contain a line "export HOME=/usr/local/home"