That is a known issue with our Apps on iOS6. They were created using the Stanza reader which is no longer supported and will not be updated. Here is a link with instructions on how to extract the ePubs from those apps to use on your device:
If you have any other questions about this, please contact our book support staff at firstname.lastname@example.org and they can assist you there. Sorry for any inconvenience this may have caused you.
Customer Service Rep,