By comparing the data in the various fields it turned out that the userdata table in my backup was missing the entries_read column. After deleting it, the import passed through smoothly and i re-created the column manually.
I have absolutely no idea why there was a difference for the new and backed up data, both claiming to be version 2.4.6.
There was versions with a broken backup function because of table columns, that got introduced in a new version but was not added to the backup and restore[/edit] functions[/edit]. But the column for the read entries, that once existed in the user data table (
entries_read) was there since ages, so I doubt, that this is a case of a forgotten table column.
On the other hand I doubt, that the backup with the list of read entries in the user data table was made with MLF version 2.4.6. This, because we introduced the new function for storing read entries in a dedicated table back in MLF version 22.214.171.124 (that was the first public beta version for MLF 2.4) and removed the column
entries_read from the user data table at that point. A backup with the column
mlf2_user_data.entries_read should have been created with an older version than 126.96.36.199.
Trenne niemals Müll, denn er hat nur eine Silbe!