[alsa-devel] Unable to find an usable access for 'default'

I'm developing a new ASOC driver, and I get this error message:

ALSA lib pcm_plug.c:729:(snd_pcm_plug_hw_refine_schange) Unable to find an usable access for 'default'

Can someone tell me what this means?

FYI, I'm in the early stages of testing my driver, and before I started I knew nothing about ALSA. This is on an embedded system, so I don't know if my ALSA installation is correct. Am I missing some kind of configuration file?