Active Directory/LDAP :: Users Right On Their Own Container?

I am trying to do something that i am sure has been done before. I have a asp.net pagethat changes a password , and it works fine if I use credentials of a user with rights to a OU that holds the users container. However i would like to have the users credentials

userEntry = new DirectoryEntry(adspath,userid,this.oldPasswordtb.Text.ToString(),AuthenticationTypes.Secure);

be used when executing

userEntry.Invoke("SetPassword", new Object[] {passwd});

currently I get System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.UnauthorizedAccessException: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED)) --- End of inner exception stack trace --- at System.DirectoryServices.DirectoryEntry.Invoke(String methodName, Object[] args) at ASP.changepassword_aspx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:usrhtmlexternalChangePasswordchangepassword.aspx:line 128any ideas why that wouldn't work users I assume have right to modify that attribute of their CN right?see code below

<%
string userid = System.Web.HttpContext.Current.User.Identity.Name.ToString();
userid = userid.ToLower();

[code]...