It doesn't take a massive leap of faith to think that the sony servers are being hammered for these free games. You ain't the only one suffering from error codes and missing games on the free list.
From sony blog
Q: I no longer have the option to choose my free Welcome Back games. What can I do?
A: If you navigate away from the Welcome Back section of the store without choosing your free games or exit the store completely you may need to follow the below in order to choose and download your free games.
On your PlayStation 3 or PlayStation Portable navigate to the PlayStation Network icon on the XMB
Log into your PlayStation Network account and choose Account Management > Transaction Management > Services List
Choose “PlayStation Network Promotions” from the list of services displayed
Select either “PS3 Free Games” or “PSP Free Games” and then choose “Select Content”
Old phatty PS3 with PS2 B/C and CFW
Old phatty PS3 with official firmware
Best of both worlds and you won't hear me bitching about the free shit we get from the scene !