Can't install apk from Package Installer
I can't believe it actually worked for me; I just tried it and it worked. Here's the solution:


Move / Copy Package Installer.apk as well as the .odex file of Package Installer from /system/app to /sdcard or whatever folder you may want to copy the file to.
Delete the Package Installer (apk and odex) from /system/app if you've copied it.
Reverse the first step. That would be, copying the copied file and pasting it to /system/app or moving it on to /system/app.
Reboot.