The reason for getting this type of update error while trying to update Windows Phone 8 is some issue with the internal scheduler which actually triggers the update every week or month or so. Now there is two option available for this issue as follows,
-> Just leave the error as of now and wait for a week or more which will automatically trigger the next cycle update and so the next time when it triggers there won?t be any conflict as such happening so that update will be proper.
-> Second option is to do the above process forcefully without waiting more. Go to the Settings -> Language & Religion -> Select ?Phone language?. Now by doing this a device rescan option will be give in the same time and hence it will start the update automatically in your Windows phone 8 and this time it will work fine without any issues.