A Definition for the Document Class could not be found

I get this confusing message every time I start a new flash project and I dont know why.

I understand what the message means, but its simply not true so that bugs me.

My project so far consists of exactly one AS file so far: CMain.as, which contains exactly one public class: CMain. The file lives here: C:\FlashProj\Game\as\CMain.as.
In my .FLA, I have set CMain as the Document class.
In File->Publish Settings->ActionScript 3.0 ClassPath, I have added “C:\FlashProj\Game\as”.
When I press “OK” from this screen, I get this message:

“A definition for the document class could not be found in the classpath, so one will be automatically generated in the SWF file upon export.”

On my last projects I think I have just ignored this message and everything worked out ok. But this time I want to know what the hell it means. My CMain class is definetly in the classpath, so what the heck is this message talking about?