Recently I was testing out Sophos UTM product and ran into a small issue that was not documented. I could not successfully install the ISO image onto my test hardware via USB thumb drive. After trying multiple downloads, multiple usb sticks and burning the image from different computers I kept getting the same error when trying to install
install.tar wasn’t found on the installation media
I found a great write up over at fastvu.com detailing the workaround.
In short, the installation needs to be told where to look for the install.tar file.
At the blue Introduction Screen press Alt + F2 to switch you to a console screen.
Mount your USB drive with the following command:
mount /dev/sdb1 /install
Press Alt + F1 to switch back to the installer to continue the installation.
Here is the link to the full how to.