I'm getting pretty desperate, so I may switch to another distribution to see if it helps...
Where I come from, we call this "Shooting on sparrows with cannons". Another distribution will use the same programs!
EDIT: I just found out that you would call it "to break a fly on a wheel". leo.dict.org is great !
Try to rip from command line to see if the backend works.
As I said before, the error message sounds like it cannot create the correct path. BTW: does the message appear right from the start, or after ripping the first song? Maybe it's a problem of the encoder (like I said above, there is also an encoder command, that needs to be set in ther correct syntax).
Maybe someone else has a suggestion, too, but I still favour the 'wrong syntax' theorie