When trying to download some recent data from my GPS, I get the following error message: "Database Error: database disk image is malformed".
That means the database (Mac TravelRecorder.db) got corrupted. You need to restore that file from your backup. It's located in either the directory "Mac TravelRecorder->LogData" or in "[homedir]->Library->Application Support->Mac TravelRecorder->LogData".
If you don't have a backup, you have to delete the current one, loose the history and consider it as a lesson.