[c#] ExecuteNonQuery: Connection property has not been initialized.

Opening and closing the connection takes a lot of time. And use the "using" as another member suggested. I changed your code slightly, but put the SQL creation and opening and closing OUTSIDE your loop. Which should speed up the execution a bit.

  static void Main()
        {
            EventLog alog = new EventLog();
            alog.Log = "Application";
            alog.MachineName = ".";
            /*  ALSO: USE the USING Statement as another member suggested
            using (SqlConnection connection1 = new SqlConnection(@"Data Source=.\sqlexpress;Initial Catalog=syslog2;Integrated Security=True")
            {

                using (SqlCommand comm = new SqlCommand("INSERT INTO Application VALUES (@EventLog, @TimeGenerated, @EventType, @SourceName, @ComputerName, @InstanceId, @Message) ", connection1))
                {
                    // add the code in here
                    // AND REMEMBER: connection1.Open();

                }
            }*/
            SqlConnection connection1 = new SqlConnection(@"Data Source=.\sqlexpress;Initial Catalog=syslog2;Integrated Security=True");
            SqlDataAdapter cmd = new SqlDataAdapter();
            // Do it one line
            cmd.InsertCommand = new SqlCommand("INSERT INTO Application VALUES (@EventLog, @TimeGenerated, @EventType, @SourceName, @ComputerName, @InstanceId, @Message) ", connection1);
            // OR YOU CAN DO IN SEPARATE LINE :
            // cmd.InsertCommand.Connection = connection1;
            connection1.Open();

            // CREATE YOUR SQLCONNECTION ETC OUTSIDE YOUR FOREACH LOOP
            foreach (EventLogEntry entry in alog.Entries)
            {
                cmd.InsertCommand.Parameters.Add("@EventLog", SqlDbType.VarChar).Value = alog.Log;
                cmd.InsertCommand.Parameters.Add("@TimeGenerated", SqlDbType.DateTime).Value = entry.TimeGenerated;
                cmd.InsertCommand.Parameters.Add("@EventType", SqlDbType.VarChar).Value = entry.EntryType;
                cmd.InsertCommand.Parameters.Add("@SourceName", SqlDbType.VarChar).Value = entry.Source;
                cmd.InsertCommand.Parameters.Add("@ComputerName", SqlDbType.VarChar).Value = entry.MachineName;
                cmd.InsertCommand.Parameters.Add("@InstanceId", SqlDbType.VarChar).Value = entry.InstanceId;
                cmd.InsertCommand.Parameters.Add("@Message", SqlDbType.VarChar).Value = entry.Message;
                int rowsAffected = cmd.InsertCommand.ExecuteNonQuery();
            }
            connection1.Close(); // AND CLOSE IT ONCE, AFTER THE LOOP
        }