If you’ve already taken the plunge and put your faith in the latest Evasi0n iOS 7 jailbreak, there’s a fairly good chance that you encounter server overload and a number of "Failed to Fetch" errors that seem to get dished out in the debug every time a package refresh is requested. This issue can be extremely problematic, but the good news is that it can be resolved relatively easily.
As you may know, Cydia is essentially an app that manages arbitrary repositories and handles the installation of packages through nominated repos. However, if any of the default repositories are offline or are having difficulty updating, then errors can be thrown up that can interfere and detract from the whole jailbreak experience. The current "Failed to Fetch HTTP/1.1 404 Not Found" errors that have been overshadowing the brand new jailbreak release are being most caused by the Ultrasn0w repository, but thankfully, a fix isn’t too hard.
Step 1: Launch Cydia and select the Manage option from the bottom tab bar.
Step 2: Select Sources from the resulting list of options. A list of installation repositories will be presented. If this is a default installation of Cydia that then list will feature BigBoss, Cydia/Telesphoreo, Dev Team, ModyMyi and ZodTTD & MacCiti.
Step 3: The problem is being caused by the Dev Team’s repository that hosts the Ultrasn0w software unlock package. Select the Edit option from the top right hand corner.
Step 4: Tap the Delete icon to the left hand side of the Dev Team repository. When a new Delete option appears on right side, tap on it to remove the repo.
Step 5: Refresh Cydia and notice that the errors have now been removed from the log.
Removing the Ultrasn0w repository shouldn’t cause any real issues for the majority of device owners. However, there will inevitably be some individuals who will ultimately rely on a software based device unlock in the future. Adding the repository back to the list is as a simple as going to Manage > Sources > Add and then entering http://repo666.ultrasn0w.com as the repository address.
It is also important to note that the ‘Failed To Fetch’ error in Cydia applies to all such repos which are either down or have temporary connectivity issues. Removing all such repos from Sources section should fix the problem.