Nexus users seem to be running into trouble with some builds of KitKat operating system. Updating to the new OS causes Near Field Communication or NFC to shut down on their devices once you update to KitKat. It affects Nexus 10 tablets, 2012 and 2013 versions of Nexus 7, Nexus 5, and Nexus 4. The bugs are present in the builds Android 4.4 (KRT16S), Android 4.4.1 (KOT49E), and Android 4.4.2 (KOT49H). Google is working on a fix for this bug and will most likely be remedied by the next firmware release.
The temporary remedy for the issue is to activate airplane mode on the device. It will let NFC work at lease once before the crash loop starts.
Source: Ubergizmo