The error is pretty clear, even if you translate it into French.
Your subquery returns more than one row. Specifically, this part of your SQL:
SELECT idBanques FROM banques WHERE sigleBanque='BCB'
Or this:
SELECT idConfigComptes FROM configComptes WHERE typeCompte='credit'
Or this:
SELECT idPersonnes FROM personnes WHERE CNI='531.1005/186.116'
If any of those return two rows, SQL has no idea which to INSERT into your new row in the
comptes
table and so it throws an error rather than risk inserting the wrong data.
At a guess, you need a join of some form, but since we have no idea of your tables and the relationships between them, or what data you are trying to insert we can;t help you any further.
Start by looking at your tables and what they contain. We can't do that for you!