It could be a lot of things. I've learned that even though we've upgraded our domino phone server, it pulls policies from our mail server. Since it's still on an old version I'm kind of thinking that might be why I get errors occasionally. Maybe that's your problem too?
Another thing I would suggest doing is reboot and try again, try on Wi-Fi, try it on your mobile connection, and try it at home. I've looked it up a little bit and a lot of people are having this same error (using pop3, exchange, ect). It might be a bug and trying it somewhere else may make it go. I'm not sure if you can tell it what you want it to sync. Maybe try syncing just you calendar would make it go and narrow down your problem as well?
Another thing I would suggest doing is reboot and try again, try on Wi-Fi, try it on your mobile connection, and try it at home. I've looked it up a little bit and a lot of people are having this same error (using pop3, exchange, ect). It might be a bug and trying it somewhere else may make it go. I'm not sure if you can tell it what you want it to sync. Maybe try syncing just you calendar would make it go and narrow down your problem as well?