Have noticed the error Failed to cache extent: ..." coming up more and more. You want to make sure that there is enough RAM on the machine and the caching gp service is allocated enough processes. Also if you start caching and keep it running in the background, it may not completely finish, but then you can click on the Job Status bar, right click the job and click Fix Errors. Also you may need to go Manage All Tiles then start caching again with the create empty tiles option selected.