Getting a connection to database lost error
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Windows.Forms;
using FirebirdSql.Data.FirebirdClient;

namespace _0912111
{
    class DatabaseConnection
    {
        private FbConnection conn;
        private FbCommand sqlCommand;
        private FbDataAdapter DB;
        private DataSet DS = new DataSet();

        public DatabaseConnection()
        {
            conn = new FbConnection("User=myuser;" + "Password=mypw;" + "Database=dbpath;" + "DataSource=serverip;" + "Port=dbport;" + "Dialect=3;" + "Charset=UTF8;");
        }
        public void showDbError(string theError)
        {
            MessageBox.Show("Could not connect to databasennError Details:n" + theError);
        }
        public FbConnection Openconn()
        {
            if (conn.State == ConnectionState.Closed || conn.State == ConnectionState.Broken)
            {
                try
                {
                    conn.Open();
                }
                catch (Exception e)
                {
                    showDbError(e.Message.ToString());
                }
            }
            return conn;
        }
        public FbConnection Closeconn()
        {
            if (conn.State == ConnectionState.Open)
            {
                conn.Close();
            }
            return conn;
        }
        public void nonQuery(string txtQuery)
        {
            FbCommand cmd = new FbCommand(txtQuery);
            try
            {
                cmd.Connection = Openconn();
                cmd.ExecuteNonQuery();
            }
            catch (Exception Ex)
            {
                showDbError(Ex.Message.ToString());
                throw Ex;
            }
            finally
            {
                cmd = null;
            }
        }
        public FbDataReader returnDataReader(string txtQuery)
        {
            FbCommand cmd = new FbCommand();
            try
            {
                cmd.Connection = Openconn();
                cmd.CommandText = txtQuery;
                FbDataReader rd;
                rd = cmd.ExecuteReader();
                return rd;
            }
            catch (Exception Ex)
            {
                showDbError(Ex.Message.ToString());
                throw Ex;
            }
            finally
            {
                cmd = null;
            }
        }
    }
}

public void nonQuery(string txtQuery)
{
    using(var conn = new FbConnection(GetMyConnectionString(...parameters...)))
    {
        using(var cmd = new FbCommand(txtQuery))
        {
            try
            {
                cmd.Connection = conn;
                conn.Open();

                cmd.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                showDbError(ex.Message);
                throw;
            }
        }
    }
}