SQL error code "Not a condition"

Does anybody know what the SQL error message “Not a condition” means?

I am trying to enter data into a table of people, and every time i get the following error:
SQL Status: S1000
Error code: -106
Not a condition in statement [INSERT INTO “People” ( “Date_entered”,“First_name”,“Gender”,“Next_position”,“Person_type”,“Surname”,“Title”) VALUES ( ?,?,?,?,?,?,?)]

Obviously I am entering or not entering something contrary to the constraints in the table (which I can’t see - see my earlier question) but I have no idea what it is.
(LibreOffice 4.2 Base / Windows 10 English)

Let’s close this one. Obviously no-one knows what the error code means, so I gave up, scrapped the entire table and re-created it.