Unidentified error

I don't know when it came and it did not affect anything, it just appear when i pressed play button. It does not only come in one project, when i made new project, it appeared again. the error message states :

Unable to convert GUI point to world ray if a camera has not been set up! UnityEditor.DockArea:OnGUI()

i hope someone can help me to explain and fix it.Thanks..

jsut save the game and restart it see.. no more error.. if u have plz contact me....

I have the same problem. Restarting dont help.

Assets>>Reimport All