HTTP 404 Error for Paper UI Only after installing .kar file


I managed to set OPENHAB2 on my QNAP and had all three UIs working. Requiring the Panasonic TV Binding, I downloaded the .kar file and uploaded it to addons on my QNAP. This appeared to work and the required Binding was visible in the Paper UI extensions. However, the Paper UI then froze, and on restarting, the Paper UI now gives me the “HTTP 404 Error Problem accessing /ui/index.html. Reason: Not Found” error. Both Classic and Basic UIs are accessible.

Does anyone have any idea how to rectify this?