You are attempting to import a cert with the same issuer/serial as an existing cert, but that is not the same cert.
Tha thu a' feuchainn ri teisteanas a thoirt a-steach aig a bheil an dearbh fhoillsichear/àireamh shreathach 's a tha aig teisteanas làithreach ach chan e an dearbh theisteanas a tha ann.