Are you perhaps trying to use it with the same old software on your computer that you used with the 110? If so, uninstall the old software then go to the Garmin site and download the software for the 405cx. If you've got the new software already installed, you can try going into the settings menu of the 405cx and do a manual 'push' of the training data over to your computer. The option is in Settings somewhere. If that doesn't work,try uninstalling and reinstalling the ANT Agent.
Hope one of those options helps you out. I only learned all of that yesterday btw, when my own 405 was having problems uploading info and I came here to ask for help...
