Restoring a backup would be good solution, but there is also the factory reset as maybe the last resort (manual page 232):
6.2. Factory Reset The Factory Reset function sets all of the configuration settings and options to their original state. All data entered after the initial installation will be deleted, including the HTTP Proxy Cache, the entire E-Mail Queue, Accounting and Reporting data, passwords, and uninstalled Up2Dates. The version of the software will not change. That is, all System Up2Dates and Pattern Up2Dates that have been installed will be retained. Factory Reset: 1. Log into the console as the Shell Administrator user. Username: root. Password: Password of shell administrator user 2. At the prompt, type the following and press Enter: cd /sbin/init.d 3. Type the following at the next prompt and press Enter: ./factory_reset reset 4. Answer the question with yes. All running processes and programs will be shut down. The Factory Reset process will continue, and the system will stop: When the process is finished, the keyboard SCROLL LED will blink, and the computer will emit a series of beeps. 5. Complete a hardware reset (Ctrl + Alt + Del or Reset). After the restart, the internal network card will use the IP address configured during installation. All passwords and configuration data in WebAdmin must now be re-installed. Backups can be restored, provided they have the correct version.
Well, someone might want to uninstall CD-ROM drive after successfull installation. Also, with the instructions almost anyone can do that, with new installation it is not always that simple. In addition, it still takes a lot less time & can almost be done remotely. But I do agree to certain state.
So you will want to cd / first, or use the option -C /. I think you want a dash before those options (tar -xIf); also I like to throw in the p option too...
no additional command line parameters are nescessary, O.K. 'p' is always a good idea but afaik not nescessary and the dash is also redundant.
If the backup was copied to '/' it would make sense to cd to '/' before running the tar command - give it a shot :-)
[ QUOTE ] From the online help
:: Encrypt Backup File ::
For enhanced security, the firewall can send the backup file in encrypted form. When activating that function, you must enter and save a passphrase. Backups created with encryption enabled will require that you enter the passphrase when you restore them. When the entered passphrase has less than 8 characters, DES will be used for encryption, otherwise Triple DES will be used.