Cant add code file to project

Hi guys

Ive been working with blueprints for abit, but would like to begin creating some class files, but when ever I go to add a new class/code file to my project I get this message :

Error : Failed to add class TestActor. Could not mark resource file for add.

What does this error mean ?

Just a guess, but it sounds like a source control problem. Are you using source control?