Hello there brigidfromca.
Messages can always be pretty daunting when we're not sure where to start. I was able to locate the following Knowledge Base article that discusses the very message you're getting:
iTunes for Windows: "Unable to load data class" or "Unable to load provider data" sync services alert
http://support.apple.com/kb/TS2690
It is a pretty thorough document with multiple steps to review, but looks to be great place to start for a resolution for you.
Thanks for using Apple Support Communities to reach out to us for answers.
Cheers,
Pedro D.