off topic BUT!:
I get the 403 issue a lot, there is a really simple way around the update issue! Consider this SOLVED!
Go to the playstore, find the app that you want to update, it will show as installed, but just click it and select your device and your phone will magically start updating!
That's a damn sight easier than performing any of the voodoo procedures I have read that people have posted, hope it helps everyone, I am just annoyed that I had not tried this method before!
Phone: Galaxy S3 i9300 / Rom: crDroid Simple 07032014
Kernel: Googy-Max2 Kernel 2.1.7 / CPU: 1.6Ghz
GPU: 700mhz / Gov: pegasusq / IO: cfq
My Univeral Samsung Mali GPU Step Calculator: http://tinyurl.com/otozlx8
My XDA threads for increasing Internal SD App Data Partition:
S2 i9100: http://tinyurl.com/pgftloa / Note N7000: http://tinyurl.com/qdtajcf