Ubuntu - USB - USB stick keep becoming read only

The USB may be in an inconsistent state, i.e. it might not have been previously properly closed, so the file system is mounted read-only to ensure no further corruption occurs.

Check and Repair a file system

fsck /dev /dev/sdg1

NOTE: A file system can only be checked when it is not mounted, so unmount first.

The Disks utility included with Ubuntu can also be used to Check and Repair.