During the upgrade process, the pre-check step is not moving forward beyond "Checking file permissions...." The upgrade appears to hang or freeze at this point, and the wizard must be canceled.
Open the file called "PermissionCheck.txt" normally located in the folder under \Vontu\Protect\updates (Windows) or /opt/Vontu/Protect/updates (Linux), from which the upgrade installation was run. You will need to comment out the "Files and Directory Replaced" section and every individual file path below it (note: under version 11 or newer, the "Files and directory replaced" line may not be present, but the file names below should still be commented out). To comment the lines, add a pound or hash symbol (#) at the beginning of the line. After doing so, save and close the file.
Finally, restart the the installation by running start_upgrade_wizard.bat (Windows) or start_upgrade_wizard.sh (Linux). Then reconnect to the wizard at https://enforce_server_address:8300/ . The upgrade should continue normally.