'function1' : cannot override inherited member 'function2' because it is not "virtual", "abstract", or "override"
A method was overridden that was not explicitly marked as virtual, abstract, or override.
The following sample generates CS0506:
namespace x { abstract public class clx { public int i = 0; public int f() { return 0; } // try this definition for f: // public int f(); } public class cly : clx { public override int f() // CS0506 { return 0; } public static int Main() { return 0; } } }