libvorbis 1.2.3 not generating 96kHz ogg file

Hi,
I'm trying to get ffmpeg (linked with libvorbis 1.2.3) to generate
a 96kHz ogg file, but I seem to be limited to 50kHz . The command
is
ffmpeg -i t16bit96kHz.wav -acodec libvorbis test.ogg
and I get the error message
[libvorbis @ 0x2051460]oggvorbis_encode_init: init_encoder failedError 
while opening codec for output stream #0.0 - maybe incorrect parameters 
such as bit_rate, rate, width or height

I tried specifying different sample rates, and anything >= 50001Hz
will give that error message.

Is this a bug with libvorbis or is ffmpeg somehow preventing
me from specifying higher sample rates ?

Thanks
CSB