Robert,
In general, you should be able to block messages to the log from within the event handler. At least, the following sequence works since TC3:
' to prevent posting the default TestComplete messages to the Log
LogParams.Locked = True
Options.Log.Enabled = False
' Handle application Login window
If Objects.Compare(Window, "LoginWindow") Then
Options.Log.Enabled = True
Log.Message ...
..
End If
' Replaces the TestComplete message with your message
LogParams.Str = "My message"
LogParams.Locked = False
Options.Log.Enabled = True
...
But there might be a problem with figuring out what exact checkpoint triggered the handler and this should be investigated.
