David, thanks for your quick reply!
I have just find a solution, I put the query in vba code with the following change:
strSQL = "SELECT Sum(CobranzasAlquiler.ImporteCobrado) AS PagosDeuda " & _
"FROM CobranzasAlquiler " & _
"GROUP BY CobranzasAlquiler.IdContrato, CobranzasAlquiler.IdTipoCobro...