I'm going to guess it's something along the lines of a Galaxy S. Samsung is the only one to do RFS file format and they stopped around the S2 time period. You need to flash back to stock with the appropriate pit file too and repartition then it might not work still but reflash without the pit and repartition checked. It really does help to state what phone for a variety of reasons though so someone can provide more detailed instructions. This was due to needing to change the partition layout to MTD for CM roms. It's not CM's fault Samsung used a stupid file system that never caught on.
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