A printing plate, and I also sent my BGS 9 RC Refractor for a crossover - they are refunding it so I dont think it was that it didnt meet the grade, after rereading PSA's rules you are supposed to submit crossovers on their own (without other cards).
The other two were the SP RC that got rejected last time for trimming (and now its too small??) and the other is a college card of Hill/Kidd which I find hard to believe is undersize.