[WD] Limits on Query execution with MySql

Hello to all

I'm trying, without any luck to run this query

sSql                is string
dsMyQuery    is data source
bRes               is boolean
bData             is boolean


sSql="SELECT r.data, G.Descrizione, SUM(r.importo_prestazione) AS tot_imp_prescr, COUNT(*) AS tot_prescr, "
sSql+="(SELECT COUNT(*) FROM registro LEFT JOIN PRESTAZIONI ON REGISTRO.TIPO_PRESTAZIONE=PRESTAZIONI.ID "
sSql+="WHERE REGISTRO.TIPO_PRESTAZIONE = 1  AND REGISTRO.data = R.DATA AND R.ID_GMT=REGISTRO.ID_GMT)  FROM REGISTRO  AS r  "
sSql+=" LEFT JOIN guardie G ON R.id_gmt=g.id " 
sSql+="LEFT JOIN prestazioni AS P ON R.tipo_prestazione = p.ID "
sSql+=" GROUP BY  r.data DESC, G.descrizione ORDER BY r.data DESC"

bRes=HExecuteSQLQuery(dsMyQuery,hQueryWithoutCorrection,sSql)

the result of "bRes" is always False !!
Trying copying/pasting the query to a client (SqlYOG), the query is executed correctly.

Also if i run the query using WDSQL tool, the result is correct and the records are shown.
Why this different behaviour?

Do am i missing something? Wrong parameters? HF query execution limits??

Tips and tricks are very appreciated.

Thanks in advance
Gianni