Disable "Stable monthly updates only" in the Updaters settings...
And about the problem when trying to apply an update: If you installed Busybox manually or SuperSU, it will update the SU binary. The updater-script checks if the SU binary is in a particular version. Of course if you updated SU in SuperSU the version is different from what the updater script expects it to be. So if you are on 2.12.7 then download the full 2.12.7 zip and open it to extract the SU file manually, then copy it to your phone and copy it from your phone to /system/xbin/ with rootexplorer or any file-manager which can write to /system
If you already updated to 2.12.14 then you need to get the SU binary from someone who has a 2.12.14 miui rom without the updated SU
Sorry to dissapoint you but its not working, i just did a full fresh install, and even after the 1st boot the OTA updates still fail.
cant we modify the OTA packages so it skips the checks and install em anyway?