I posted something about this in the Marvin forum a while back, but you can get around the malformed database error if you go to the Marvin section of the main system Settings app, going down to the Advanced Support And Maintenance section (Support and maintenance), ignoring the scary warnings and tick the Optimize database toggle, then start Marvin (if it's already open force quit it from the Multitask Switcher before you do this) and connect to Calibre as normal. It might throw an error dialog but it should actually load the catalog on the device and let you use Calibre as normal. Until the next time...
