Not sure whats happening as it was a-o.k. a few days ago. Tried launching after a couple changes to no avail.

Then I get the silly idea to connect to the internet and try again.

It launches without a hitch.

What exactly would cause this? And if needed, what would be the best way to provide proof of the issue?

Video soon

Uninstalled, re-installed, no dice.

Odd, with no net connection, if I start it twice (run two instances) it will launch the second instance. However, upon quiting, the first failed launch does not close.

If I connect to the web with the failed instance still there, that instance will start immediatly upon connection

The simple solution is to use Task Manager to kill the first instance of the game, then you needn't connect to the internet :)

This is an issue for me with Gothic 3, so far as I've been able to research, seems to be related to Microsoft's software certificate revocation needing online checks.

Are you using Windows 7? It specifically starts the internet client for connected gaming. Every time you start a game, for the first time after a re-boot, it will spawn this process. Just ignore it (as you did), or delete it in the task manager. You will, of course, need to start a new instance of the game, since the game will hang until the internet connection successfully resolves, which is not going to happen.