iPad Collections and Calibre Series

Hi all,

I'm trying to get Calibre to export to iTunes to sync with the iPad. The syncing works except the series are not being converted to iBooks collections. I believe the problem may be related to a custom field I have created in Calibre to remind whether I have read the book or not (copied from a post on this forum). When Calibre transfers the book to iTunes everyone has a Category of "PLUGBOARD TEMPLATE ERROR Value: unknown field #read".

Is there any way of fixing this as I'd like to use Calibre to organise the iOS collections without sacrificing this useful "Read" field.

TIA