Hi Supermario - you might want to provide more information, e.g. iPad model, computer being used (i.e. PC, Apple, or other), and whether this is a new problem (i.e. have you been able to sync in the past to iTunes?). You might want to 'restart/reset' your iPad, check that you have the latest version of iTunes, and even possibly delete and reinstall iTunes.
Pleast let us know if any of these suggestions help - do them in the simplest order first - good luck!