I'm having what appears to be a bug issue also.... I'm trying to encode a voice recording using the preset as foolows:
--abr 56 -mm %d
fb2k has always wanted the "%d" there in the past so I wasn't surprised about that... but whenever I try to convert PCM WAV's with these settings it gives me a general file error as folows:

I'm on WinXP SP2, foobar .9 beta 11, and using lame 3.97b1...
I tried my normal music setting which is:
-V 2 --vbr-new
and everything works fine... I've never tried to encode audio at this level so I maybe missing something, but can anyone else either tell me if I'm doing something wrong or confirm this bug...?
FYI: I used EAC to convert the same WAV's using the same "--abr 56 -mm" string (w/o the %d) and it worked fine... also, I have Lame in a seperate directory but have pointed foobar to it (and as stated above, it works fine in the other preset)
Peace
Ross