Import from V6 databases failed with "SQL logic error ... table category.Categories has no column named fixedName"

Cannot upgrade to V7 because my databases are not migrated.
Unfortunately, I entered my mail adress at first startup which deleted my whole database with thousands of mail mesages from the past years.
Fortunately, I could restore it from a backup, BUT this is a V6 backup and I’m not able now to upgrade to V7 because of this error.

After investigating the database tables structure from V6 Mails, I found that there are 2 files dealing with categories in V6: one is called “categories.dat”, the other is called “category_index.dat”.
Both of them have a table “Categories”, but the “category_index.dat” file also holds a table for the relationships between categories. AND the data is the quite the same in both “Category” tables, except that the “Category” table from file “category_index.dat” seems to have the “right” structure (one more field with the name “fixedName”).

So what I did:
   1. rename “categories.dat” to “categories.old”
   2. copy “category_index.dat” and rename to “categories.dat”
   3. delete complete V7 data folder (“C:\Users<username>\AppData\Roaming\eM Client”)
4. start emClient V7
5. skip entering mail addresse, etc.
6. re-import V6 mails from backup folder (with changed “categories.dat”)

–> everything OK.

Maybe I lost some of the categories which I inserted in pre-V7, but I don’t care, I’ve got my mails back.

br, WM