FOP FO to MIF transformation not working?

Hi,

I may be missing something obvious, but FOP version 0.20.2 does not appear to run MIF conversions. I attempted to convert simple.fo from  examples/fo to MIF and received the following output:

fop simple.fo -mif simple.mif
[INFO]: FOP 0.20.2
[INFO]: building formatting object tree
[INFO]: rendering areas to MIF
[INFO]: [1]
[ERROR]: null

All other formats work fine. Do I need to any special FO directives for MIF to process?

Thanks,
Peter