Lynda, Have you downloaded the spreadsheet?
When you do that you can whack everything down on mass but in the new interface layout when you add a new redirect you can add a file name which doe not exist in there too.
Goolgle can slap you on the wrist if it realises those pages never existed and your trying to do redirects.
Thanks for the information Liam. I got it now => Also most of the pages I am redirecting were never indexed by Google so I am not too concerned.
I have a similar issue.
We are negotiating with a client who has a ecommerce site on ZenCart, a php opensource cart. He has been running this website for a while and is concerned about drop in rankings if he moves to BC. Please guide how we can convince him, and also maintain his SEO after moving to BC.