If you're specifically looking to play PES 2011:
If your internet connection fails during online activation, the game may offer a "Manual Activation" option. pes 2011 serial unlock request code
Is downloading a PES 2011 crack illegal? Legally, yes—if you do not own the original media. However, Konami no longer sells PES 2011. They do not support it, and they have not issued a patch to remove the unlock server requirement. If you're specifically looking to play PES 2011:
If the game could not verify the license online, it would generate a unique "Request Code" based on your hardware ID. Users were then directed to a Konami web portal to enter their Serial Key and Request Code to receive an "Unlock Code" for offline activation. Current Status of Activation pes 2011 serial unlock request code