Normaly I use my Debian Installation-usb-drive in school at school Computers. But now I Got this output. It works at home and Updates didn't help.
Normaly I use my own labtop in school (because we all have to) but there areas without wifi and there are just this old win7 Pentium Computers wich take 10 Minuted to boot up. So I always used Linux USB drive to make them usable.Are you using a different computer at school to use the USB stick on, than you would normally do?
On the most of this Computers USB Boot is disabled, but there are some Left.Perhaps the school's IT department disabled the USB ports?