The user would also be notified for NO [ALERT], right? So the only difference is closing the connection? How might that help?
If the server *knows* that the error is such that it simply cannot continue to perform any useful operations, it might as well just shut down of its own accord (maybe this will release some resources that are contributing to the problem), and thus a BYE is warranted.
If the server thinks it's dealing with a transient error, or knows that the error relates to an operation on a specific object, and therefore that operations on other objects are likely to succeed, a NO response is the correct one, since the server is offering to carry on operation.
BAD is only issued when the server detects a protocol syntax error.
--lyndon
