Hello,
Brian, I guess you have already this case: the Catalina 202/K shot down by merchant ship(s) of convoy KMS-3 on 20 November 1942, but the link below is providing extensive details:
http://www.202-sqn-assoc.co.uk/files/friendly_fire.pdf
But the story gives not the serial of the Catalina, so if anybody has it I will be interested.