I've just noticed that since upgrading to CPG 1.3, the 'URL' link in the File Information section wasn't working correctly, when it was under CPG 1.2.1
e.g. here's a link that was on one of my images...
http://www.sirjohn.co.uk/gallerydisplayimage.php?pos=-1258
It should be...
http://www.sirjohn.co.uk/gallery/displayimage.php?pos=-1258
i.e. a '/' is missing between the install directory and displayimage.php.
It's fixable by changing the setting "Target address for the 'See more pictures' link in e-cards" in the config to add a '/' to the end of the URL, however I hadn't changed this setting so something changed it or it now requires the '/' at the end. I did change a setting in the config so maybe saving the settings altered it, or maybe the upgrade did.
You're on the right track - the behaviour from the "Target for ecards" field has slightly changed from cpg1.2.1 to cpg1.3.x; it now needs a trailing slash. Please add the slash and you should be fine.
GauGau