nothing magic if the midi file is fine...
load the midi from floppy into memory, turn the write protection off, and save title with all file save options off and sequencer only on.
It's easier to do floppy copies, if you have done this, and there is nothing wrong with the midi file, try saving that individual file again, in case there was a hiccup in the copy operation.
this is the save procedure.
if your sequencer song is in technics format as opposed to midi just do performance save instead. You can selectively save to advantage but to start off with this is as good as anything.