>(Sets the currently indexed attachment - its value can range from zero to object.AttachmentCount)

Close, its Zero to the Count minus 1.

>Does anybody know of a cleaner way to do this ? I don't want to code my ONERROR routine to catch an error based on its message text.

Hmmm, I don't remember having to do it this way, are you sure you're looking at the message you think you are?