Recording error within XBMC with Tvheadend

Hi

I've got the Pulse Eight install running on the latest XBMCbuntu and it's working great, except when I try recording from XBMC I get an error "PVR backend error". xbmc.log gives me this:

22:09:33 T:4358320 ERROR: PVRClient - AddTimer - addon 'HTS Tvheadend:127.0.0.1:9982' returned an error: server error

There is nothing in the Tvheadend logs. Recordings started from the Tvheadend web interface work great.

Any ideas?

tia