Edited to correct a mistake:
Originally Posted by COFFEE BOY
thanks, I did not know you could do that. - how do you do that?
You can (for example) copy a file from the hard drive to the Cruzer. I assume you don't have the root password set and so need to use the sudo command.
If the Cruzer is mounted as /dev/sdb1 and you want to copy the file testfile.txt, open a terminal and navigate to the directory which contains textfile.txt and enter
sudo cp testfile.txt /run/media/username/devicename
("username" in the path is your username and "devicename" is the identifier for the Cruzer) where /run/media/username/devicename is the mount point of the USB drive (in my installation of Slackware, it may be different in Ubuntu but you can find it from the GUI using your file manager). On my PC, for example, the mount point for a Sandisk drive inserted by user boris is /run/media/boris/B013-238C .
You will be asked for your user password. If the file is copied then the problem is caused by your not having permission to write to the drive as a normal user.
Apologies for the error.