PHP Timestamp Question

For reasons unknown, the CMS script that I am using is no longer displaying the correct time. It began on January 1, 2011.

Once the server hit January 1, 2011, all of the new posts began reading December 31, 1969, which I think is the mysql default.

Any date entered prior to January 1, 2011 WORKS, but any date beyond that comes up with the old date error.

Any ideas>?

What version of PHP are you using?