Facebook support was only added in 10.8.2. Are you using 10.8.2 yet? If so, what specific error code are you getting? We're not mind-readers.
If you read the headers as you're supposed to do, you'll see that -requestAccessToAccountsWithType:withCompletionHandler:
does not exist on Mac, and is deprecated on iOS. You should be using -requestAccessToAccountsWithType:options:completion:
.