This is the error I get in openMSX.
I am using openMSX v.17 under Linux, emulating Philips NMS 8255
I have set in catapult -> DiskA: /home/david/msx
I can read but obiously not save.
Well, did you check if the folder has occupied more than what the floppy of the emulated machine supports? If it does, it is full indeed, that is seem as a Floppy with a floppy file system by msx dos...