[WARNING] can't keep up! Did the system time change or is the server overloaded

Ok, not much info to give u other than my console is contantly getting spammed with this message even when there is no one on the server. I have no idea why. Im running the server with mcmyadmin if that makes a difference, and it seems this has only been happening since the recent minecraft update. Also i never had any lag before the update but now it is terrible. Any ideas?