I would like to know is patent "US6323569 B1" still valid? its end date?
If you look in http://portal.uspto.gov/external/portal/pair (enter the number without the "US" and "B1") as "Patented case" and the next fee payment window closes on 11/27/2013. The patent is valid. You will also be able to see that it had quite a stormy path to its acceptance which resulted in a certificate of correction.
If the maintenance fee is paid, the patent will expire on 11/3/2019, 20 years after the effective filing date.