I have tested with a backed up version of 1763795278 (which has had automatic updates on it disabled via adding a steam.cfg) and it works 100% fine, once it upgrades to 1766177208 I can no longer connect to any dedicated servers for the game and see this error:

"This steam account has been used to log in from another computer. To continue using steam, you need to log in again"

The issue is directly caused by the new client update... I tried to contact steam support and it wasn't taken seriously, I ended up just closing the ticket after the response, but they said the development team check this section out!

As a workaround quite a few members of the ges community have locked our steam versions to 1763795278 and are able to connect to servers once more... but this isn't ideal, please could you confirm if you are still wishing to allow functionality for windows users for source sdk base 2007 mods, because nfo (a server rental company have been informed, are aware of this issue and may delist the product for hosting if it's not resolved; as well as currently the discord community of Goldeneye: Source (which reports keep coming in of this issue for those which haven't received a copy of the older client or managed to lock it before the update) we are seeing this issue come up by everyone who plays since the newest Steam Client update.

Thank you for your help and understanding in this matter,

Leon