Running two SQL commands results in one not being executed

List<string> PDToDelete = new List<string>();
SqlConnection sqlConn = new SqlConnection("Server=" + config.DBHOST + ";Database=" + config.DBASE + ";User Id=" + config.DBUSER + ";Password=" + Decrypt(config.DBPASSWORD) + ";MultipleActiveResultSets=True");
sqlConn.Open();

SqlCommand checkIfFileExist = new SqlCommand("SELECT Pruefdatei FROM Pruefdatei_Import", sqlConn);
SqlDataReader reader = checkIfFileExist.ExecuteReader();
if (reader.HasRows)
while (reader.Read())
{
    string path = reader.GetString(0);
    FileInfo pruefDatei = new FileInfo(path);
    if (!pruefDatei.Exists)
    {
            PDToDelete.Add(path);
    }
}
reader.Close();

foreach (string entry in PDToDelete)
{
    if (MessageBox.Show("Die Prüfdatei " + entry + " existiert nicht mehr. Sollen dazugehörige Datenbanksätze gelöscht werden?", "Löschen bestätigen", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
    {
        using (SqlCommand deleteEntriesFromDB_1 = new SqlCommand("DELETE FROM Pruefdatei WHERE Referenznummer = @PDN", sqlConn))
        {
            SqlParameter pathParam = new SqlParameter("@PDN", entry);
            deleteEntriesFromDB_1.Parameters.Add(pathParam);
            //This one doesn't work
            deleteEntriesFromDB_1.ExecuteNonQuery();
        }
        using (SqlCommand deleteEntriesFromDB_2 = new SqlCommand("DELETE FROM Pruefdatei_Import WHERE Pruefdatei = @PDN", sqlConn))
        {
            SqlParameter pathParam2 = new SqlParameter("@PDN", entry);
            deleteEntriesFromDB_2.Parameters.Add(pathParam2);
            deleteEntriesFromDB_2.ExecuteNonQuery();
        }
    }
}
sqlConn.Close();