I just had this exact same problem. This will sound crazy but if someone sees this try this before drastic measures. delete method signature:
public static void main(String args[])
(Not the body of your main just method declaration)
Save your project then re-write the method's header back onto its respective body. Save again and re-run. That worked for me but if it doesn't work try again but clean project right before re-running.
I don't know how this fixed it but it did. Worth a shot before recreating your whole project right?