When trying to update on line from earlier version ( in this case 1.346 ) this msg is showed :
Failed to upgrade from /webmin_1.350_all.deb : Cannot downgrade to version
Just in case, I have tried download the 1.350 version, and then upgrade from local file, same msg .
upgrading with dpkg works fine .
Logged In: YES
user_id=129364
Originator: NO
If you run the command :
dpkg --info /webmin_1.350_all.deb
on your system, what does it output?