There are a few possibilities. For me, i was using an external hard drive. Brand new xbox, and the USB connection was faulty. The games that installed on the internal would work fine, but the ones on the external always seemed to either not wanna install or fail/error. The only fix ive found is to pause ALL updates, and hard reboot the xbox (hold down the power button until the xbox turns off), then start ONLY the download you want up. Let it finish before starting the others. You can also (if you are using an external), switch it to a different port. Other than that, you could have a faulty hard drive (even brand new ones can be faulty).