Serial numer never catch up in photoshop CS2?

my Photoshop CS2 30 days trial period expired. and I got the keygen exe. It gives the serial no. When I enter the serial number and click the "Activation Option" link, it will give me an error. it says " You must enter a valid serial number before activating online....". So Please help me to activate the photoshop CS2. I do not wants to install any other versions.