Repairing WU with the Windows Repair suite:
Download & Install Windows Repair from this link (here).
Open Windows Repair, select the Repair – Main tab and click on Open Repairs.
In the Repairs window, use the drop-down menu under Repairs to select the Windows Updates preset. Once the repair strategies are selected, click the Start Repairs button and wait for the process to complete.
Restart your computer and see if you see the same error message when you apply the Windows update.