I have just merged some new tables from our VDF 7.3 development into our VDF 15.1 development. When I went to add the data-dictionaries, and that's after I had manually migrated them to the new format, I got the error The Data Dictionary Data has not been initialized and rejects the file.
The only way I managed to to add the DDs was first create a New DD and then open the file and replace the contents with one I was trying to add and save. Afterwards the Table Editor was happy to drop the DD and add it back with no error.