DM6 gives Program Error after migrating V5 data

[JohnThomson]

I started up a new install of DM6, and it offered to migrate my V5 data. The first migration failed, I think because DM5 was running, though it didn't tell me that, only that the file was locked. I stopped DM5, restarted DM6, and did an import, but as soon as it was complete I got an error message. As near as I recall, it was the same one I now get every time I start DM6: I see a little window with an animation saying "Starting the Donor Manger", and in front of it a window with the caption "Program Error" and message "Field name is a duplicate or invalid" (Cancel/Ignore/Help). Cancel quits the program. Help does nothing. Ignore seems to get me in successfully, but it is worrying.