a lot of us use google sync using google calendar to sync our calendars and you must have a gmail acct to be able to do this. usually if there is an error most often times than not the wrong acct is being synced.
Also, for those of us who synchronize our devices with Microsoft Outlook (BIS users who have to plug the device into the computer), you can only synchronize one Calendar so whatever you have set as your default account is going to be the one that sync's with Outlook.
