can't find the error source

First of all - I’m a C# newb. The console gives me “Undefined Queue: ‘Opaque’” error. When I double-click it, nothing happens, so I can’t find it’s source. Searching the Internet, I learned that the error is due to a “problem with a shader”, whatever it is. How do I fix it?

As here is said, this error is caused by a shader. Do you remember which objects did you add to your escene just before you start getting this error? Any of them is using a custom shader that has Queue=Opaque instead of Queue=Geometry (at this point I don’t know what I’m talking about because I don’t know anything about shaders coding). I think you must look shader by shader in order to find which is the one that causes the problem or if you don’t want to inspect shader code just try to remove the last objects added to the scene in order to find it. Good luck!

I have waited for the user “tanoshimi” to re-post his comment as an answer. Since he didn’t do so, I’ll answer the question myself.
The solution was to use the Ctrl+Shift+F and search the whole project for the word “Opaque”. I then located the shader file on my hard drive and deleted it. Of course, I left a backup in the very same folder packed up in a RAR-file, so that Unity doesn’t read it.
Problem solved.

TANOSHIMI, if you’re reading this, post your comment as an answer and I’ll accept it.