I assume you are using a NanoBSD image on the CF card, you should be.
It expects by default to mount the root partition from the primary IDE master but fails in your case.
Not a problem. I expect it said 'type ? for boot options' or something similar. Enter ? and you should have a list you can choose to boot from including, maybe only, the secondary slave.
Enter that and it will boot. Possibly:
Once it has booted edit the fstab to make the change permanent.