Originally Posted by Amiga4ever
I've used (new) floppy disk which was formatted as 720k disk to transfer files...
Are you using DSDD (1.0MB unformatted capacity) or DSHD (2.0 unformatted capacity) floppy disks for this task? Depending on the exact model of floppy drive you have in your Amiga, it may not read DSHD reliably, even when DOS-formatted to 720K capacity.
If you are using DSHD disks, try it instead with a DSDD disk to see if it solves the problem.