Error # was raised, but no message with that error number was found in sys.messages

I received this alert from one of my customer's servers today:

   Msg 18054, Level 16, State 1, Line 1

   SQL Server Alert System: 'Severity 016' occurred on \\SQLSERVER11

   DESCRIPTION: Error 778441, severity 16, state 1 was raised, but no message
   with that error number was found in sys.messages. If error is larger than 50000,
   make sure the user-defined message is added using sp_addmessage.

Odd.  I didn't know who or what is trying to raise an error with a msg_id that doesn't exist yet, so I ran this to search all database objects for any reference to 778441:

     SELECT o.name, o.id, c.text, o.type

     FROM sysobjects o RIGHT JOIN syscomments c 

       ON o.id = c.id

     WHERE c.text LIKE '%778441%'

It returned to me this trigger:

If we look at the trigger definition, you can see where the unknown msg_id's are being called:

   CREATE TRIGGER [dbo].[tblOrderItems_ITrig] ON [dbo].[tblOrderItems] FOR INSERT AS

   /* PREVENT INSERT IF NO MATCHING KEY IN 'tblItems' */

   IF (SELECT COUNT(*) FROM inserted) !=

      (SELECT COUNT(*) FROM tblItems, inserted WHERE (tblItems.ItemID = inserted.ItemID))

       BEGIN

           RAISERROR(778441, 16, 1)

           ROLLBACK TRANSACTION

       END

   /* PREVENT INSERT IF NO MATCHING KEY IN 'tblOrders' */

   IF (SELECT COUNT(*) FROM inserted) !=

    (SELECT COUNT(*) FROM tblOrders, inserted WHERE (tblOrders.OrderID = inserted.OrderID))

       BEGIN

           RAISERROR(778450, 16, 1)

           ROLLBACK TRANSACTION

       END

   

Take a look in sys.messages to confirm that they don't exist:

   

     SELECT * FROM sys.messages WHERE message_id IN (778441,778450)

What is the fix?  I just run this to create two new user defined error messages using the numeric identifiers in the trigger:

     USE master; 

     GO 

     EXEC sp_addmessage

        @msgnum = 778441, @severity = 16, @msgtext = 'There is no matching key in

        tblItems, the insert may not be performed.', @lang = 'us_english', 

        @with_log = 'TRUE';

     EXEC sp_addmessage

        @msgnum = 778450, @severity = 16, @msgtext = 'There is no matching key in

        tblOrders, the insert may not be performed.', @lang = 'us_english', 

        @with_log = 'TRUE';

With these new error messages, the msg_id numbers are now known, and the sev 16 alert goes away.  

See this for more details on sp_addmessage:

    https://msdn.microsoft.com/en-us/library/ms178649.aspx