Problem with opening more than 5 proteins for superimposition in DS 2.5

Hello. I'm using version 2.5 of DS and trying to superimpose many proteins at the same time, like I used to do with DS 2.1. But I can't insert more than 4 protein molecules (the first one being the fifth) - the program simply doesn't insert them. All files are working. Could someone please assist? Thanks.