First they wanted more info and wrote this:
Thank you for contacting Retrospect Technical Support. After reading over your issue I understand that you are having issues with Retrospect backing up to your optical drive. In order to troubleshoot this problem for you I will need you to provide me with some additional information. Are you receiving any error messages, and if so what are they? If you could take screen shots and send them to me that would be very helpful. Also what type of DVD drive do you have, and is it recognized by other applications? Is Retrospect the only application that isn't seeing your optical drive.
Then they wrote this:
You can check our hardware compatibility list to see if your devices on our list. It can be found at www.retrospect.com/hardware.
Also in some rare cases, you may want to create a custom configuration that overrides Retrospect's built-in recognition. You should use this procedure only if you are experiencing difficulty backing up to a CD/DVD drive or you are not getting the performance you feel the drive is capable of. While customization may improve communication between Retrospect and the drive, it may not.
In the navigation bar, click Configure>Devices. Click the Environment tab, select the CD/DVD drive you want to reconfigure, then click the Configure CD/DVD button in the toolbar. In the dialog that appears, click Configure, then follow the on-screen prompts to create a custom configuration for the drive.
You can do the same procedure on a mac by going to the Storage devices tab highlighting the device then control clicking and choose create cd configuration
Now, if I was working in technical support I would have known that the bloody thing doesn't work with optical drives because it has been turned off in the program! Could have saved me a lot of time and hassle!!!