Since I had installed iOS5, when syncing my iPhone with iTunes and Outlook on Windows, I got the error message :
“Unable to retrieve conflict information from sync server. Please try again next time conflict resolver window is presented”
or in French:
“Impossible d’obtenir les informations sur les conflits depuis le serveur de synchronisation. Veuillez réessayer à la prochaine présentation de la fenêtre de résolution des conflits.”

You may have this message because you have activated iCloud on the iPhone, on iTunes, but not on Windows. To solve this you need the iCloud Control Panel for Windows :
Search for iCloud in the Windows search bar. If you don’t have it, you can download it here.
Launch the iCloud program and simply enter you iCloud login / password. Select what you want to synchronize with iCloud (Mail, Contact, Calendars, bookmarks or pictures flow). Apply. Then go back to itunes and sync your iphone or iPad. It should work better but prepare to have some duplicates in your calendars or contacts.

If you have too many duplicates, for instance for your contacts, first make sure you have a backup of your contacts, a backup independent from iTunes. Then one option is to turn off iCloud / Contacts, to delete the iCloud contacts, then to synchronize and finally you reactivate iCloud / contacts and you resynchronize.

One more thing, don’t forget you can directly check what is on iCloud by going to https://www.icloud.com/.

I hope it helped.