OnServerEvent error always popping up?

Whenever i run my game an error will always pop up, It says:

15:09:08.552 - OnServerEvent can only be used on the server

Since i became a bit annoyed and worried because of the error i tried to create a "Test place" with no scripts, Even when i run it there the problem still remains.

Is there anything i can do about it?

There's more lines of code in the console that suggests that the error is in a core script which explains why it happens in every game.

Has anyone else encountered the same problem lately?

OnServerEvent is the event that tells the server that an event has been sent from the client. OnServerEvent can only be used in Scripts, not LocalScripts, as it is server-side, not client side. For more information, view this article.

http://wiki.roblox.com/index.php?title=Remote_Functions_%26_Events

You might want to browse through your plugins; if you did as you claimed, which is open up a completely empty place, with no script, and roblox still gives you that error/warning; you might have a corrupt/virus plugin.