IPad Air cannot be backed up to iMac using iTunes

[zo_zo65im]

Once a week I back my new iPad Air to my iMac all of which run the latest available software. On plugging in the iPad this time around I got the followng message: "Itunes cannot read the contents of the iPad. Go to the summary tab in iPad preferences and click restore to restore this iPad to factory settings"

How can I backup my iPad or what must I do to restore my iPad. I do not keep an iCloud backup, only an iMac backup. Thank you