LDAP User password change

Question

I am trying to do code for ldap current user password change but I am getting a null value in PrincipleContext for the context, so the user principle errors out saying "bad user or password"

using (var context = new PrincipalContext(ContextType.Domain))
                using (var user = UserPrincipal.FindByIdentity(
                                  context, 
                                  IdentityType.SamAccountName, 
                                  Microsoft.SharePoint.SPContext.Current.Web.CurrentUser.LoginName))
                {
                    user.SetPassword(NewPwd);
                }

Any help?

I want to basically change the current users password from a webpart.

Thanks