DRM removal isn't working for me either. I'm using an iPhone (5.1.1), Requiem 3.3.6, and iTunes 10.5.2.11 on a PC. The problem is that this particular ebook was made for iPad only, so I can't authenticate for use on my iPhone. Requiem says:
The following files could not be decrypted: Making of Star Wars (Enhanced.ibooks(Key not found. Can you read this book?)
I'm guessing we need an iPad.
-G