Thats why I think Firewall, The Updater is a separate .exe and firewall in windows often block based on .exe
They all go out to a website for checking version.. normal web request to port 80.
Windows have a built in firewall, or you disable it ? if the built in is on, You can try to temporary disable it and see if it work. if it does.. go to advanced firewall settings and you probably finds a entry for MultiCommander
When a program do network stuff, windows pops up a message asking if it is allowed. If you pressed 'no' Windows adds a block in the firewall for that program.
The only logical reason for the MC not finding new version and Updater do.. Is that something is blocking MC from doing it.