Had a similiar error with july updates, installed also manually . My fix was to uninstall them one by one and check WU for the error, after WU worked again i installed them via WU and this time no error appeared.
But I didn't get error of installing all updates manually. By the way, these updates installed after making new install of windows 8.1 update 1. In previous installation of windows 8.1 update 1 I installed The old August Update manually and I didn't got error.
Had also no errors during install ... still WU was broken with that damned error and no fix worked, except uninstalling and re-installing via WU. At least your decision ... you still can wait for a miracle to happen .
This might be a case in which the installation order and reboots were required. Make sure you have the latest servicing stack installed (KB2975061) Then, install them in the correct order:
I found solution : In Windows Update -> change setting -> download updates but let me choose... I made this change after installing windows and before checking for updates. This option allow to me to install updates manually and after that choose what to install via windows update.