USB Read-Only Filesystem

I wanted to extend john smiths answer. I had made two USB sticks bootable using Ubuntus "Start media creator". It made the sticks unusable afterwards, because they were write protected and I could not format them in Ubuntu or Windows. I tried fdisk, gparted. No dice.
What helped was inserting the stick (make sure this is the only USB drive inserted), finding out where it is mounted:

df -Th

That will show you a list of devices/partitions and their mount paths/points: udev devtmpfs 7,8G 0 7,8G 0% /dev ... /dev/sdb1 vfat 7,5G 4,0K 7,5G 1% /media/<USER_NAME>/<STICK_NAME_OR_ID>

Find your USB stick and remember its partition device path (here: /dev/sdb1) and mount point (here: /media/USER_NAME/STICK_NAME_OR_ID). Then unmount it:

sudo umount /media/USER_NAME/STICK_NAME_OR_ID

Now recreate the file system (FAT32 in this case):

sudo mkfs.msdos -F 32 /dev/sdb1

Wait a short time and unplug the stick. Wait again and plug it in. It should be writable now...