Throwing a general exception type such as System.Exception or System.SystemException in a library or Framework forces consumers to catch all exceptions, including unknown exceptions that they do not know how to handle (see FAQ: Why does FxCop warn against catch(Exception)? for reasons as to why this is bad).
Instead, either throw a more derived type that already exists in the Framework, or create your own type that derives from Exception.
The following list examples of when you should throw specific exceptions:
When validating a parameter (including the value parameter in the set accessor of a property) that:
is a null reference (Nothing in Visual Basic)
is outside the allowable values for a enum
contains a format that not meet the parameter specifications of a method (such as the format string for ToString(String))
is otherwise invalid (such as an empty string)
When an operation is invalid for an object's current state:
When an operation is performed on an object that has been disposed:
When a conversion would result in an overflow (such as in a explicit cast operator overload):
For all other situations, consider creating your own type that derives from Exception and throwing that.
Note: Exceptions that derive from ArgumentException (including ArgumentNullException, ArgumentException, ArgumentOutOfRangeException and InvalidEnumArgumentException), InvalidOperationException (including ObjectDisposedException) and NotSupportedException should only be thrown in situations that are avoidable (such as passing a null argument) and if thrown, would indicate a bug in the calling code. The Path class is not a good example of this, it incorrect throws ArgumentException to indicate that a path is incorrectly formed, however, it does not expose any methods that can help prevent this from occurring.