active directory findone() method
DirectoryEntry de = null;
            SearchResult results = null;
            de = new DirectoryEntry();

            //geting the result FROM ad
            de.Path = dr.manager;
            de.AuthenticationType = AuthenticationTypes.Secure;
            DirectorySearcher search = new DirectorySearcher(de);
            search.Filter = string.Format("(objectClass={0})",'*');
            search.PropertiesToLoad.Add("IsraelID");
            results = search.FindOne();
            de = results.GetDirectoryEntry();

System.Runtime.InteropServices.COMException (0x80004005): Unspecified error

   at System.DirectoryServices.DirectoryEntry.Bind(Boolean throwIfFail)
   at System.DirectoryServices.DirectoryEntry.Bind()
   at System.DirectoryServices.DirectoryEntry.get_AdsObject()
   at System.DirectoryServices.DirectorySearcher.FindAll(Boolean findMoreThanOne)
   at System.DirectoryServices.DirectorySearcher.FindOne()

string LDAP = "LDAP://DC=MYDOMAIN,DC=COM";
using (DirectoryEntry dirEntry = new DirectoryEntry(LDAP, null, null, AuthenticationTypes.Secure))
    using (DirectorySearcher dirSearch = new DirectorySearcher(
        dirEntry,
        string.Concat("(objectClass=*)"),
        new string[] { "IsraelID" }))
    {
        SearchResult result = dirSearch.FindOne();
        if (result != null)
            return result.Properties["IsraelID"][0].ToString();
        else
            return null;
    }

DirectoryEntry de = null;
SearchResult results = null;
de = new DirectoryEntry();

// Assuming your domain dns name is treyresearch.net
de.Path = "LDAP://servername/CN=users,DC=treyresearch,DC=net";
de.AuthenticationType = AuthenticationTypes.Secure;
de.Username = "treyresearch\Administrator";
de.Password = "P@$$W0rd";
DirectorySearcher search = new DirectorySearcher(de);
search.Filter = string.Format("(objectClass={0})",'*');
search.PropertiesToLoad.Add("IsraelID");
results = search.FindOne();
de = results.GetDirectoryEntry();

/* Connection to Active Directory
 */
DirectoryEntry deBase = new DirectoryEntry("LDAP://WM2008R2ENT:389/dc=dom,dc=fr", "jpb", "Pwd");
//DirectoryEntry deBase = new DirectoryEntry("LDAP://WM2008R2ENT:389/dc=dom,dc=fr");

/* Directory Search
 */
DirectorySearcher dsLookForOUs = new DirectorySearcher(deBase);
dsLookForOUs.Filter = "(objectCategory=organizationalUnit)";
dsLookForOUs.SearchScope = SearchScope.Subtree;
dsLookForOUs.PropertiesToLoad.Add("cn");
dsLookForOUs.PropertiesToLoad.Add("ou");

SearchResultCollection srcOUs = dsLookForOUs.FindAll();

foreach (SearchResult srOU in srcOUs)
{
  Console.WriteLine("{0}", srOU.Path);

}

de.path=dr.dr.manager

de.Path = "LDAP://"+dr.manager;