A common mistake is to apply the wrong update file to the wrong software version, this is harmless.
Another is that the update file was corrupt because it was not fully downloaded or because the firewall disturbed it,
this is also harmless.
Having the power cable pulled out of the NTB after the update file was uploaded and before the reboot was complete
may result in serious problems and the unit may need to be returned to the factory to have the software reloaded.
There may have been a completely unforseen error.
Instructions
Connect to the NTB with with your web-browser.
If all you see in the browser is an Index of files then FTP the update file into the "updates" folder,
pull the power cable out of the NTB and put it back in again.
This is a last resort action, if it does not work then the NTB must be returned to the factory to have the software reloaded.
If you saw the NTB's Home Page then browse to "Setup | Support Tasks | Extras | Package Installations"
(or "Settings | Support | Package Installations" in version 4).
Look for lines in the update log that contain the word "ERROR", these may give you an indication of what went wrong
allowing you to try the update again.