Earlier today many people had difficulties connecting to Xbox Live, which has now been fixed. But what caused this sudden outage? Well, according to Microsofts blog, it was all due to a human error. Below is the quote direct from the blog, posted by Eric Neustadter.
The root cause of this outage was human error. A change resulted in an interruption to normal traffic flow within our datacenters, which logged users out and prevented them from logging back in. We're sorry for this, and we'll be updating our processes to prevent this from happening again in the future.
Thankfully the problem was shortlived, and everything is back online and working.