Welcome to LQ. Make sure that the little "write protect" slider on the floppy is set to the "unlocked" position (meaning that writing is allowed.
Alternatively, what kind of data is on the floppy, and what exact mount command are you issuing? If the floppy is FAT32 you might try
Code:
mount -t vfat -o umask=000 /dev/fd0 /mnt/floppy
which tells the system that the filesystem type is FAT32 and that you want to mount it with 777 permissions