I'm stuck trying to boot from a CF card (Sandisk Extreme III 8GB) connected to a Promise Ultra66 mounted in my Asus PVI-486SP3.

The Ultra66 card is detected properly and I get the Promise BIOS screen, the card is also detected in UDMA4. I have booted from a floppy and partitioned the card with FDISK, and installed MS-DOS 6.22 without problems.

The problem is my system hangs where usually "Starting MS-DOS..." comes up, the message doesn't come up and the cursor just blinks there...
When I boot from a floppy I can access the card, and I can run software from it no problem. I ran speedsys and the results seem pretty good (about 25MB/s read speed, the card is rated 30MB/s). I just can't seem to boot from it. The CF-IDE adapter also has DMA connections wired between IDE and CF.

I have tried an old 512MB card too, and Promise detects it as PIO2. I installed MS-DOS and the system boots fine from this old card. I have also tried a Kingston 16GB card, and this was also detected as UDMA4. But, no booting from this card also.

I have disabled all onboard IDE stuff, disconnected the CD-ROM, removed all cards except VGA card and Ultra66 card. I have also tried updating the Ultra66 BIOS with version 2.0 from the Promise website.

Any ideas what else I could try?