Issue Updating Google Apps - "Not Signed Correctly"

First and forehand, I am running JB 4.2.2 AOKP on my AT&T Samsung Galaxy S3. I have the latest gapps package installed after every time I flash an update to my ROM. For some reason though, whenever I try to update either Gmail or Play Music, I get the error "Package file was not signed correctly. Uninstall the previous copy of the app and try again." I can't uninstall the apps because they are used as system apps, and the best I can do is disable them, but that still didn't let me update them. I'm sure it has something to do with the gapps package that I flashed, but why does it not give me the same error when I update Play Movies and Play Magazines? I do not use Titanium Backup to back up any of my apps, so I saw that that was a problem for some other people. If however, there is another question that relates more to mine, I will be glad to go and check it out, but after my looking I did not find a solution to my specific problem. Thanks in advance! **EDIT:** Here's the link to the [gapps package](http://www.task650.jocoje.com/Gapps/gapps-4.2.2-jb-6.12.2013-signed.zip) that I installed as well as the [exact ROM](http://forum.xda-developers.com/showthread.php?t=1766684) I am using.