Comment 6 for bug 1260712

TL;DR you can ignore the error message - the device will still update just fine after a reboot.

In order to fix Bug #1217098, I made a change to the ApplyUpdate() D-Bus method, as described in Bug #1247215. This was communicated through the ubuntu-phone mailing list, but no human or automated check was in place to make sure system-settings was prepared for the change. That's a subject for a different discussion.

All it means though is that system-settings is not getting its expected empty return string after calling ApplyUpdate(), but in the predominately most common case, the device will successfully reboot and apply the changes, so any return value is mostly useless anyway (except for the user confusing error message). So, no functionality is broken, but we unfortunately do show this confusing message.