I must have done something wrong. I have a C# project in Visual Studio 2008. All of a sudden I see a lock on my classes and when I hover the class names on the top tab I see the class name as : C:\Myprojects\Oder.cs[Read Only] !
Has something weird like that happened to you before?
A couple of possibilities spring to mind:
Have you added the project to source control?
Have you marked the project folder (and all it’s sub folders) as read only?
Of course, someone else may have done either of these things if they have had access to your machine.