What roms are you trying to flash? On hboot 1.50 you should be able to flash jellybean and Gingerbread roms.
Harmonia is an exception as I think it's coded to work on both hboots, but if you are trying to flash other ice cream sandwich based roms, you need hboot 1.58.
Are you doing a full wipe before flashing? Wipe all partitions (except sd card)?
What recovery are you using?