Erro com acessos simultâneos

public class clsDados
    {
        private static string strConexao = ConfigurationManager.ConnectionStrings["strConn"].ConnectionString;
        private static SqlConnection conexao = new SqlConnection(strConexao);

        public SqlConnection fechaConexao()
        {
            if (conexao.State != ConnectionState.Closed)
            {
                conexao.Close();
            }
            return conexao;
        }

        public SqlConnection abreConexao()
        {
            if (conexao.State != ConnectionState.Open)
            {
                conexao.Open();
            }
            return conexao;
        }
    }

public class clsBusca
    {
        public DataSet BuscarResultados(string Texto_Busca)

        {
            clsDados objDados = new clsDados();

            SqlCommand comand = new SqlCommand("BuscarResultados", objDados.abreConexao());
            comand.CommandType = CommandType.StoredProcedure;

            SqlDataAdapter adapter = new SqlDataAdapter(comand);
            comand.Parameters.AddWithValue("@Texto_Busca", Texto_Busca);

            try
            {
                DataSet dataSet = new DataSet();

                //Atualiza o dataSet
                adapter.Fill(dataSet);
                return dataSet;
            }
            catch (SqlException ex)
            {
                throw new Exception("Erro encontrado: " + ex.Message);
            }
            finally
            {
                objDados.fechaConexao();
            }
        }
    }

<connectionStrings>
		<add name="strConn" connectionString="Data Source=XXX.XX.XX.XXX;Initial Catalog=XXX;Persist Security Info=True;User ID=XXX;Password=XXX;"/>
	</connectionStrings>