The Updates Configurtion file...will be downloaded...only if it's newer than the one on the target machine
Then after describing what happens if the file is moved around and restored on the server, it says...
the moved/restored file "...will be ignored because it is older than the error message
Eh? So why does the Updater change its strategy from comparing the dates between files on the target machine and server to comparing the date on the error message and the file on the server?
The paragraph you are referring to explains the case in which the updates configuration file is moved and then placed back in the original location.
When the Updater checks for updates, it downloads the updates configuration file. The next time the Updater checks for updates, it also checks if the dates of the downloaded file and of the file on the server are the same. If the dates are the same, the updates configuration file on the server was not modified, so there are no new updates.
If the updates configuration file is moved on the server, accessing its original URL will return a HTML page with the "404 - Page not found" message. Since this HTML is generated when the Updater tries to access the URL, it is always newer than the downloaded file. In this case the HTML is downloaded and the Updater tries to check it (an error will be shown because it's not a valid updates configuration file).
When moving the updates configuration file back in its original location on the server, the file will be older than the HTML page with the "404 - Page not found" message. In this case the Updater will ignore the file on the server. The solution is to modify the updates configuration file so the Updater downloads it over the HTML with the error.
Basically, the behavior is always the same: compare the file downloaded on the machine with the file on the server. However, the file downloaded on the machine can be a HTML with an error instead of a TXT file with the update information.
