How-To Geek

Sometimes, no good reason. They usually will be successful another time. It could be as simple as whatever it was updating was busy at the time.

If it only happens on occasional updates then check in 'view update history', double-click the failed update(s) and amongst other things it will give you an error code. Sometimes clicking the 'help with this error' will give a link to the reason for it, but if not then just Google the error code. From there you'll be able to decide whether it is something you should worry about or something that will right itself eventually.