Compiler Error CS1900

Warning level must be in the range 0-4

The /warn compiler option can only take one of five possible values (0, 1, 2, 3, or 4). Any other value passed to /warn will result in CS1900.

The following sample generates CS1900:

// CS1900.cs
// compile with: /W:5
// CS1900 expected
class x
{
   public static void Main()
   {
   }
}