I dunno, RX50 format is easy to copy. Make sure that
your 1.2M drive
is declared as such in the BIOS setup--if it's confused with a 1.44MB
drive, it's not going to work, as 2D operation on a 1.2MB requires a
write clock (300KHz) that conforms to a 360 RPM drive. A 1.44MB
drive is 300 RPM--so any attempt to write a 2D format using a 250KHz
clock rate is guaranteed to fail--you'll run out track before you run
out of data.
I once saw a PC multi-I/O card that couldn't do the 300kbps data rate, I
think it just did it as 250kbps.... Needless to say that card went
straight back to the suppliers...
Anyway, with so few people (other than on this list :-)) using 5.25"
drives now, I wonder if most modern PCs can still generate the 300kbps
rate, If not, this could explain the problems the OP is having...
-tony