Did you download without a factory reset or signing out of the Kobo account? If so, you have probably lost the Dictionary table from the database. This is no longer needed and isn't created in the recent firmware versions.
The following is the definition. Running this with your favourite SQLite tools should fix it.
Code:
CREATE TABLE Dictionary (
Suffix TEXT,
Name TEXT,
Installed BOOL,
Size TEXT,
LastModified TEXT,
IsSynced BOOL,
PRIMARY KEY(Suffix)
)
I don't think you need to insert anything. That should be done during a sync.