Subform data problem in LibreBase

Today, eventually, I managed to solve a critical problem with Mysql Direct Connector (see this post), but even though now I can see tables and queries in my odb, I still get an error message when I open a form with a subform.
This is the error message:

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ':link_from_ID_classe ) ORDER BY "ID_classe", "cognome", "cognome" ASC' at line 1

And the syntax is this

The SQL command leading to this error is:

SELECT "studenti"."ID" AS "ID", "studenti"."cognome" AS "cognome", "studenti"."nome" AS "nome",             
"studenti"."data_nascita" AS "data nascita", "studenti"."abitazione" AS "abitazione", "studenti"."via" AS "via", 
"studenti"."telefono" AS "telefono", "studenti"."origine" AS "origine", "studenti"."ID_classe" AS "ID_classe", 
"studenti"."dati_personali" AS "dati personali", "studenti"."situazione_scolastica" AS "situazione scolastica", 
"studenti"."voto_matu" AS "voto matu", "studenti"."significativita" AS "significativita" FROM "miei"."studenti" "studenti" 
WHERE ( "studenti"."ID_classe" = :link_from_ID_classe ) ORDER BY "ID_classe", "cognome", "cognome" ASC  

Therefore now I see, in my form, the main form (correctly), but the subform is empty.
What should I do?

Solution here:

«have a look at the content.xml in the *.odb-file (could be opened by a zip-program)

Not working code:
<db:driver-settings db:system-driver-settings="" db:base-dn=""

Working code
<db:driver-settings db:system-driver-settings="" db:base-dn=""/>
It works!