Failure to sync Calendars via iTunes

I'm fairly new to iPads, having only bought one 24 hours after the "3" became available in the UK.

I run an i7 iMac under OSX.6.8 Build 10K549 and sync via iTunes v10.6.1 (7) and the iPad is running iOS 5.1.1 (9B206)

To start, all went well apart from a glitch with my Address Book which failed to update on the iPad, a problem resolved by AppleCare's "second tier" techies who identified a corrupt Address Book Group hader.

However, a short while ago, I found that iCal and Calendars were only syncing one way - changes on the iMac were reflected on the iPad but not vice versa.

Tonight, I discovered that no syncing was taking place with calendars at all - a new entry on the iPad didn't reach the iMac and a new appointment on the iMac didn't reach the iPad.

So, perhaps unwisely, as the iMac was more up to date, i decided to take a risk the and use iTunes > iPadDevicesname > Info > Advanced > Calendars option which, according to iTunes would: During the next sync only, iTunes will replace the selected information on this iPad with information from this computer.

Which sounded fine to me and just what the doctor ordered.

But ...

... there's that dreaded word but again ...

... but ... my iPad Calendars were all wiped, vanished, gone, disappeared!

I have also noticed, although it may always have been thus, that the Sync Calendars panel in iTunes has "All calendars" selected and yet the list of Calandars is totally blank! Which may, of course, explain why "nothing" has been carried over.

I have tried syncing via both wifi and USB and I cannot get my Calendars back on to the iPad!

What has happened? How can I get my calendars back on the iPad? How can I ensure that syncing is a two way street via iTunes?