VB.NET receiving no response from PostgreSQL 9.3 when inserting duplicate record

I have migrated from PostgreSQL 8.3 to PostgreSQL 9.3 in order to use the improvements implemented in this version. With version 8.2 I had no problem handling errors when trying to insert a duplicate record with unique key since the program (Visual Studio 2013 vb.net) received a message from PostgreSQL and acted accordingly with a TRY...CATCH. But since I have migrated to 9.3, when doing a insert, the program waits to receive a message from PostgreSQL 9.3 and does not continue. I attached example code:

Public Sub EjecutaComando(ByVal StringSql As String)
    'Procedure básico para ejecutar Insert i Updates sin tenerlas que implementar en cada uno de los procesos
    Dim data As New NpgsqlCommand
    data.Connection = MiConexio
    data.CommandText = StringSql
    Try
        AbrirConexion()
        data.ExecuteNonQuery()
    Catch ex As Exception
        nada()
    Finally
        CerrarConexion()
        data.Dispose()
    End Try
End Sub

If the statement is insertagainst a table with a unique key, the code stops at data.ExecuteNonQuery(). I run the query from PgAdmin and it returns an error message of duplicate Key. The Npgsql version I use is 2.012.0.

Can someone enlighten me where the problem is?