Hi,
If you have setup the Administrative HTTP or HTTPS servers to run in "server mode" instead of the default "inetd mode" under Services->Network, http, Configure, undo that, as during the firmware upgrade procedure the webUI will not display the upgrade progress or errors.
Another side effect is that after hitting StopAll under System Utilities, Services, the webUI will stop responding. If that happens, telnet or ssh the box and login as the 'root' user, same password as the webUI, and issue the 'rcall start' command.
FIX: under Services->Network, http, Configure, set both the Administrative HTTP and HTTPS server to run in "inetd mode".