ActiveDirectoryMembershipProvider - 无法联系指定的域或服务器

Question

我需要验证给定LDAP连接URL和服务帐户的用户。但是，当我只是进行目录搜索时，我看到了不同的行为，它运行得很好，并且正在执行Membership.GetAllUsers（），它失败并且“无法联系到指定的域或服务器”

private static void GetUsers()
{
    // this succeeds to list all users
    DirectoryEntry de = new DirectoryEntry()
    {
        Path = "LDAP://serveraddres/DC=BLAH,DC=COM",
        Username = "validusername",
        Password = "validpassword",
    };

    DirectorySearcher srch = new DirectorySearcher(de)
    {
        Filter = "(objectClass=user)"
    };

    using (SearchResultCollection results = srch.FindAll())
    {
        foreach (SearchResult res in results)
        {
            Console.WriteLine("\t{0}", res.Path);
        }
    }

    // Below fails with 'The specified domain or server could not be contacted.'
    foreach (var user in Membership.GetAllUsers())
    {
        ... do domething
    }
}

这是web.config中的配置 - connectionString和MembershipProvider

    <add name="IAMConnectionString" connectionString="LDAP://serveraddres/DC=BLAH,DC=COM" />

    <add name="AspNetActiveDirectoryMembershipProvider"
      type="System.Web.Security.ActiveDirectoryMembershipProvider, 
        System.Web, Version=2.0.0.0, Culture=neutral, 
        PublicKeyToken=b03f5f7f11d50a3a"
      connectionStringName="ADConnectionString"
      connectionUsername="validusername"
      connectionPassword="validpassword" enableSearchMethods="true"
      attributeMapUsername="sAMAccountName"
         connectionProtection="Secure"
         />

为什么DirectorySercher工作正常，但Membership.GetAllUsers（）没有，使用相同的服务帐户？