Editing an existing Note on a bug screen actually works fine. It seems to save, then redirects to the "Operation Successful" notice. But then instead of going back to the Bug page (which it does when adding a New Note) it instead throws the specified error: APPLICATION ERROR #203

So to clarify the steps to replicate:

1) Go to a bug page
2) Go to an existing Note
3) Click the "Edit" button against the Note
4) Edit the note and press the "Update Information" button
5) It will redirect to "Operation Successful" screen
6) It will then redirect to the ERROR screen

I hope this is clear enough...