Evasi0n has released an updated version of their untethered iOS 7 jailbreak through Cydia. Jailbreakers that jailbroke with Evasi0n7 version 1.0.1 need to update to this version as soon as possible. This version of the untethered jailbreak has changes in it that Saurik requires for getting cydia and MobileSubstrate up to operational status.
To install the new version of the untether navigate to the changes tab in cydia as shown below.
image credit: iclarified.com