Rename Anchor Points
Say you want to apply the 3D (Classic) Rotate effect to a complex illustration but you have a rogue anchor point that causes this message: An unknown error occurred. Click MORE INFO and try some of the solutions to fix the issues.
It has taken me many hours to figure out that a single anchor point (that is neither part of a shape or a path) is the most-likely cause of this error message. I work very clean, but rogue anchor points happen occasionally and it's incredibly frustrating to find.
The solution is to search through all your objects and find the single point. The issue is when you view all your objects in the Layers panel, a complete path (that does not cause issues) and an incomplete anchor point (that does cause issues) are both named <Path>.
I propose that single anchor points get renamed in the Layers panel as <Anchor> and not <Path> so that the error can stand out to someone searching for a rogue anchor point in 1000+ individual objects.
Hannah Wantz commented
While this is an interesting proposal indeed, you should not forget about the Object > Path > Clean Up command, which shows to delete single points automatically. No manual search is required!