The ezAgenda and ezwebin (web interface for 3.9) have a bit different classes. The Calendar class is equal, but the event class have an xml block instead of a text block and image atrribute.
One suggestion would be to implant the classes used in ezwebin and then patch over the changes you want from ezwebin.
http://packages.ez.no/ezpublish/3.9/
For the ones upgrading from eZagenda to ezwebin I would think the easiest is to use one of the extensions for changing text_block to xml_block and simply removing the image attribute.