I came across a similiar problem when I got message related to invalid label of USB then
As one of senior members suggested to me
You can comment line containing /dev/sdb1 ( by prefixing # ) in /etc/fstab & append following
/dev/sdb1 /pendrive vfat defaults,user,noauto 0 0
Provided there is a folder named /pendrive.
Now , no need to go root for mounting , copying & unmounting USB.Just do as normal user.
Also system will not prompt you when you insert USB so that you can plug out USB before you ran 'mount /pendrive' or after you ran 'umount /pendrive'.
If you find this useful than thank me by pressing thumbs up button.Thank You.
$#lines beginning with # are for explanation only no need to type them in terminal
$#access USB in your file manager
$#Now you can eject USB