为什么Assembly.GetType()返回null，求大神指点

我有一个程序片断
Assembly a = Assembly.LoadFrom("BaiduMusic.dll");
Type type = a.GetType("CMusicSearch.BaiduMusic.MainSearch ", false);
调试运行，a可以得到{BaiduMusic, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null}，
不过不知道为什么type一直为null

BaiduMusic.dll中类MainSearch 的定义如下

namespace CMusicSearch.BaiduMusic

{

    using CMusicSearch.ISearch;

    using CMusicSearch.MusicCommon;

    using System;

    using System.Collections.Generic;

    using System.Text;

    using System.Text.RegularExpressions;



    public class MainSearch : IMusicSearch, IEncoding

    {

        /// <summary>

        /// 获得TR块中每个TD块信息(歌曲地址、歌曲名、歌手名)

        /// </summary>

        private readonly string BAIDU_MUSIC_INFO_PATTERN = "<td class=tdn>.*?</td><td class=d><a href=\"(?<LinkUrl>.*?)\"\\s+target=.*?>(?<MusicName>.*?)\\s*</a></td><td>(<a.*?>(?<Singer1>.*?)</a>.*?)?(<a.*?>(?<Singer2>.*?)</a>.*?)?(<a.*?>(?<Singer3>.*?)</a>.*?)?(<a.*?>.*?</a>.*?).*?</td>";

        /// <summary>

        /// 获得TR块中每个TD块信息(专辑名)

        /// </summary>

        private readonly string BAIDU_MUSIC_INFO_PATTERN_2 = "<td class=al>(<a.*?>(?<Album>.*?)</a>)?.*?</td>";

        /// <summary>

        /// 获得Baidu网页中所有歌曲信息的TR块的正则表达式

        /// </summary>

        private readonly string BAIDU_TR_PATTERN = @"<tr>\s*<td class=tdn>.*?</tr>";



        /// <summary>

        /// 创建音乐获取URL

        /// </summary>

        /// <param name="info">音乐搜索信息</param>

        /// <returns>URL</returns>

        public string CreateMusicUrl(SearchMusicInfo info)

        {

            try

            {

                string format = "http://mp3.baidu.com/m?f=ms&rf=idx&tn=baidump3&ct=134217728&lf=&rn=&word={0}&lm={1}";

                return string.Format(format, new object[] { info.MusicName + CommonSymbol.SYMBOL_SPACE + info.SingerName, info.MusicFormat.ToString("D") });

            }

            catch

            {

                return string.Empty;

            }

        }



        /// <summary>

        /// 分析返回的DIV快内的歌曲信息

        /// </summary>

        /// <param name="tr">歌曲tr块的HTML信息</param>

        /// <returns>TR块中歌曲信息列表</returns>

        private List<MusicInfo> MusicInfoBuild(string tr)

        {

            List<MusicInfo> list = new List<MusicInfo>();

            tr = tr.Replace("\n", string.Empty);

            GroupCollection groups = RegexHelper.GetRegexGroup(tr, this.BAIDU_MUSIC_INFO_PATTERN, RegexOptions.IgnoreCase);

            if (groups != null)

            {

                MusicInfo info = new MusicInfo {

                    MusicSource = "百度音乐",

                    MusicName = EncodeConverter.HtmlDecode(groups["MusicName"].Value),

                    Album = EncodeConverter.HtmlDecode(RegexHelper.GetRegexGroupItem(tr, this.BAIDU_MUSIC_INFO_PATTERN_2, "Album", RegexOptions.IgnoreCase)),

                    SingerName = groups["Singer1"].Value + " " + groups["Singer2"].Value + " " + groups["Singer3"].Value

                };

                string str = groups["LinkUrl"].Value;

                if (string.IsNullOrEmpty(str))

                {

                    return list;

                }

                List<string> musicUrlList = MusicOperator.GetMusicUrlList(str);

                if ((musicUrlList == null) || (musicUrlList.Count == 0))

                {

                    return null;

                }

                List<string> list3 = musicUrlList;

                foreach (string str2 in list3)

                {

                    if (MusicOperator.urlIsValid(str2))

                    {

                        MusicInfo item = info.Clone() as MusicInfo;

                        item.MusicUrl = str2;

                        item.MusicFormat = MusicOperator.GetMusicFormat(str2);

                        list.Add(item);

                    }

                }

            }

            return list;

        }



        public List<MusicInfo> PageAnalysis(string PageContent)

        {

            List<MusicInfo> list = new List<MusicInfo>();

            try

            {

                List<string> list2 = RegexHelper.GetRegexStringList(PageContent, this.BAIDU_TR_PATTERN, RegexOptions.Singleline | RegexOptions.IgnoreCase);

                if (list2 == null)

                {

                    return list;

                }

                foreach (string str in list2)

                {

                    list.AddRange(this.MusicInfoBuild(str));

                }

            }

            catch

            {

            }

            return list;

        }



        /// <summary>

        /// 指定当前页面编码方式

        /// </summary>

        /// <returns></returns>

        public Encoding PageEncode()

        {

            return Encoding.GetEncoding("GB2312");

        }

    }

}