I was about to say what wallabybob is saying…
I ran into some issues with my Atom boxes in terms of which RAID mode to choose, how to handle failures, etc... and in my experimentation, I am pretty sure I ran into the same error as you... mostly, in the case of when I had to drives RAIDed usign the built in RAID functionality (either Intel or ADaptec, in my case just the RAID feature built into the BIOS, not a hardware raid), then switched that functionality off to plain old IDE functionality (I'm using SATA drives). It appeared that pfSense just locked up mid boot... looks like it was looking for RAID controller drivers to initialize. It would just sit there mid boot.
This is why, I posted a question regarding this matter and what i was doing wrong... the overall response was to use the built-in OS based RAID features... since I could drop the drive into another box and it should still boot... This is what I am doing now for production environments.
It was also enough of a convincing issues to do the same thing on my Asterisk box.
Hope this helps.