I just started getting these errors out of nowhere on code that has been running forever. I cannot get any additional information as double clicking on the errors shows nothing. And it just showed up all of a sudden.
Where do I even start looking?
Usually, this happens when an element in the Inspector fails to update properly through the rendered scene when the preview window (Play) is not running in Unity. It’s a lot common thing when modified things such as UI colors or sprites are modified.
It can also happen when you script things that affect text content (such as fonts, sizes, etc.)
Since this isn’t a system breaking error, but mostly a Warning.Log text about something that has happened in Unity’s inspector rendering pipeline so it will not affect your project. It’s more like a “Hey! I failed doing this, but then I succeeded through another pass” message.
The common full method to “fix” this thing (until it appears again for whatever reason) as it is kinda stressing to see that red ! symbol is to close each opened script in either MonoDevelop or Visual Studio, then clean & rebuild (in the options) so that your scripting program clear its memory from any useless crap it might have temporary registered.
Then, you save your scene and close Unity. Make sure it’s fully closed (especially if you’re on Mac) with nothing still running in the background. Reopen Unity afterwards.
If it still does it, try loading another project… even if it’s a bland state project with as little as 1 scene, 1 script (so that Unity can “rebuild” both type in its system) and then close it… re-open in your current project. This is the best way of forcing Unity at recompile whatever might have been corrupted or its inner errors.