Could not complete the move. The items may have already been dele

That's the message we get when we try to move one particular email from a
user's inbox to a public folder. The email can be deleted and restored back
to the inbox, so clearly it's really there.

Two 'unusual' things about this email:

1) It has an attachment that's a little over 10mb in size.
2) That attachment is blocked, however, so this user can't detach the
attachment and try to save that way.

I suspect this attachment is causing the problem, but don't know why it
would. Anyone know the cause or a work-around? We'd like to move that email
to the Public folder.

Thanks,
Dave