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.
As of November 27, 2013, this patent had lapsed due to a Failure to Pay Maintenance Fee. As of January 14, 2014, US 6,323,569 is expired and is no longer enforceable, with an effective date of November 27, 2013.
Nov 3, 1999 AS Assignment Dec 24, 2002 CC Certificate of correction May 5, 2005 FPAY Fee payment Year of fee payment: 4 Apr 29, 2009 FPAY Fee payment Year of fee payment: 8 Jul 5, 2013 REMI Maintenance fee reminder mailed Nov 27, 2013 LAPS Lapse for failure to pay maintenance fees Jan 14, 2014 FP Expired due to failure to pay maintenance fee Effective date: 20131127