Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Shared Photo Streams and VIP Mail Comes To iPhone 3GS In iOS 6 Beta 3
When iOS 6 launched we knew there was going to be some restrictions regarding what iOS 6’s feature work on what device and we found a lot of the big new features not to be compatible with the iPhone 3GS or lower.
As of yesterday when Apple released iOS 6 Beta 3 to developers it seams that Apple have been working on making more and more features available for the iPhone 3GS. The iPhone 3GS now has the options to support shared photo stream and also the VIP Mail feature