event Error (Command as String, Error as String)
Occurs when the server failed to response to the client's command.

TypeDescription
Command as String A string expression that indicates the command that fires the error.
Error as String A string expression that indicates the description of the error.  
Use the Error event to monitor the errors that server sends to the client. The LastError property retrieves the errors based on the connection, not on the server side. If the Error event occurs, the Error parameter contains the error code, and the error description. The RFC 977 describes the errors that a news server gives. 

The following sample displays the error that server replies, when LIST2 command is sent. The LIST2 command is not a valid command, that's why the server replies: "500 command not recognized":

Dim WithEvents n As EXNNTPLibCtl.NNTP

Private Sub Form_Load()
    Set n = New NNTP
    n.Connect "news.devx.com"
    Debug.Print n.Command("LIST2")
    n.Disconnect
End Sub

Private Sub n_Error(ByVal Command As String, ByVal Error As String)
    Debug.Print "Error: '" & Command & "' " & Error
End Sub