change password AD using asp.net

[bemytthm]

I just want to ask abt communicate with AD using ASP.net. I would want to ask you all to help me correct a problem like this:

This is a code i use to change password on AD

public bool ChangePasswordAD(string strLogin, string strOldPasswd, string strNewPasswd)
    {
        try
        {   string domainAndUsername = "aloha.com" + @"\" + strLogin;
            DirectoryEntry entry = new DirectoryEntry(ConfigurationManager.AppSettings["LDAPpath"].ToString(), domainAndUsername, strOldPasswd, AuthenticationTypes.Secure);
            DirectorySearcher searcher = new DirectorySearcher(entry);
            searcher.Filter = "(&(objectCategory=person)(objectClass=user)(sAMAccountName=strLogin))";
            SearchResult objResult = searcher.FindOne();
            DirectoryEntry objLoginEntry = (objResult != null) ? objResult.GetDirectoryEntry() : null;
            if (objLoginEntry != null)
            {                    
                object obj = objLoginEntry.Invoke("ChangePassword", new object[] { strOldPasswd, strNewPasswd });
                objLoginEntry.CommitChanges();
                obj = null;
            }
            entry = null;
            searcher = null;
            objResult = null;
            objLoginEntry = null;
        }
        catch (Exception ex)
        {
            return false;
        }
        return true;
    }

The problem here is :

- If the Admin creates a user and don't check " User must change password the next logon " then the user from client can change password successfully , and without error
- But if the Admin creates a user and check " User must change password the next logon " then the user can't change password .
I know the error caused by : When "User must change password the next logon" is checked, user have to change it immediately in a sign in window, and use new password to login instead of the old password .
How can I deal with this problem ?
Thanks you.

[semomaniz]

Please read

http://www.codeproject.com/KB/system/everythingInAD.aspx#46

[bemytthm]

i already read it. But it didn't help.
The problem here is
if i had an DirectoryEntry object , i could easily do eveything such as finding, setting properties, getting properties, and so on..
But when the admin checked that property like that, i cann't login successfully to use DirectoryEntry object.