I used to run SageTV (software PVR) which had a hardware extender. As my RasPi is mainly for XBMC, I'm considering reusing the extender as a case. There's enough room such that I could probably run cables from the ports on the RasPi to the existing cutouts on the SageTV box, and it would fit better ...
I'm getting the same error as you. I have the same firmware version, just build yesterday. Before trying the .deb I built the source, but it too produced the "Failed to add service."
I enabled log level 3, but xbmc.log doesn't reveal much. I can post it if needed..