Steve,
From the Calibre site (
www.calibre-ebook.com) FAQ section...
Follow these steps to find the problem:
•Make sure that you are connecting only a single device to your computer at a time. Do not have another calibre supported device like an iPhone/iPad etc. at the same time.
•If you are connecting an Apple iDevice (iPad, iPod Touch, iPhone), use the ‘Connect to iTunes’ method in the ‘Getting started’ instructions in Calibre + Apple iDevices: Start here.
•Make sure you are running the latest version of calibre. The latest version can always be downloaded from the calibre website.
•Ensure your operating system is seeing the device. That is, the device should show up in Windows Explorer (in Windows) or Finder (in OS X).
•In calibre, go to Preferences->Ignored Devices and check that your device is not being ignored
•In calibre, go to Preferences->Plugins->Device Interface plugin and make sure the plugin for your device is enabled, the plugin icon next to it should be green when it is enabled.
•If all the above steps fail, go to Preferences->Miscellaneous and click debug device detection with your device attached and post the output as a ticket on the calibre bug tracker.
There's a lot of other advice in there so that's where I'd start.
SteveJ