I haven't come across that error before, I'm afraid. Are you saying you cannot launch the Asset Editor? FYI, you would launch it from within ModBuddy. With a project open, it's via Tools --> Asset Editor.
If you're getting an error that fundamentally prevents a mod from being built, it could be that the installation either didn't work as expected, or something in the paths isn't configured correctly. I would expect the Asset Editor to install as a component of the Civilization VI SDK Tools - the same installation that results in you having ModBuddy.
It could also be that you are referencing art assets in your mod, somehow, that it cannot reconcile (and is producing an error that is not very intuitive). But, again, I'm speculating - I've never seen the error before.