Thank you for the information. I've already done that several times. I'm working on this issue for a long time already.
The last thing that came into my mind is the differences between two version 18.7.2354 builds 18.7.4041.389/18.7.4041.0
I managed to run Avast FREE after clean install using offline installer version 17.2.2288. But after automatic updates it went to 18.7.2354 build 18.7.4041.0 and the "Failed to load UI" error came back.
The only Windows XP SP3 machine that works has version 18.7.2354 builds 18.7.4041.389. When trying to update this working machine it says that it already has the latest Avast FREE version and does not change to build 18.7.4041.0
If someone could provide me with download link to version 18.7.2354 builds 18.7.4041.389 I would gladly test it and hopefully solve this Failed to load UI issue once and for all
