Well, a good online update function is nice, if it's not working it's a PITA....
With versions older than 2.2.2, the update file download from sourceforge fails on Windows, because apparently it's redirected to https which makes the http download library check certificates. Unfortunately, the root certificate file isn't present when packaged for Windows, so this step fails with a weird error message.
Actually, all update downloads are cryptographically secured in the Admin4 update module itself, verified against a built-in public key. Consequently, it's no risk to use http instead of https, or (when redirected to https) ignore certificate information. Admin4 online update now does the latter.
So when you're running on Windows, the online update won't succeed. To fix this, you can either download a full installation package or patch the existing installation. If you're unsure, it's recommended to use the full installation package.
If you want to patch, it works like this:
Download Update-2-2-2.py from sourceforge, rename to Update.py and replace the the old version in the Admin4 directory. Now, the update should complete successfully. Don't try to restart, just cancel and close Admin4. After restart, you should be up-to-date.