Keep in mind, as other posters mentioned, EVERYTHING in the Sony Classics list that counts for the credit (at least that I saw, and I went through a lot of it!) is *Public Domain*. In other words, these are books that can be freely distributed by anyone without penalty. What Sony has done is processed them to the format for the reader, and added a price. So they're giving you 100 free books that were free to begin with, but claiming that it's a $199 value.
Many of these books are also available here in the proper format, and from what I understand, formatted far BETTER than the ones from the Sony store. So if you can't get access to the credit, don't worry about it. Really. You can get the same content elsewhere for free without registering the reader.
In fact, you don't have to register the Reader at all as long as you use non-DRM content. Or you could buy LIT format with DRM, remove it using a tool that is mentioned frequently, then convert the non-DRM LIT to the Sony format using the excellent libprs software.
The libprs software, by the way, is FAR BETTER than the Sony software. I grabbed a couple things from the Sony store, but am probably not going to use their software any more at all, and just stick with libprs.