Hi again, @linuxis4me 
Hmmm... Try to run the "Startup Disk Creator" from the command line, with "sudo", so it runs with administrator privileges (to see if that makes a difference), by using the following command:
sudo usb-creator-gtk
By the way, I got this idea of starting the Startup Disk Creator from the command line, using "sudo", from the most upvoted answer in the following discussion:
I hope this helps