Exception.Message contains only the message (doh) associated with the exception. Example:
Object reference not set to an instance of an object
The Exception.ToString() method will give a much more verbose output, containing the exception type, the message (from before), a stack trace, and all of these things again for nested/inner exceptions. More precisely, the method returns the following:
ToString returns a representation of the current exception that is intended to be understood by humans. Where the exception contains culture-sensitive data, the string representation returned by ToString is required to take into account the current system culture. Although there are no exact requirements for the format of the returned string, it should attempt to reflect the value of the object as perceived by the user.
The default implementation of ToString obtains the name of the class that threw the current exception, the message, the result of calling ToString on the inner exception, and the result of calling Environment.StackTrace. If any of these members is a null reference (Nothing in Visual Basic), its value is not included in the returned string.
If there is no error message or if it is an empty string (""), then no error message is returned. The name of the inner exception and the stack trace are returned only if they are not a null reference (Nothing in Visual Basic).