According to the log file "Did not find QFE hotfix matching KB2685813" there's an issue with this Hotfix.
Either it's not properly installed, or it cannot be detected as already installed.
I can't tell you for sure how to fix this, but what you may try (after taking a snapshot) is to download the hostfix from https://www.catalog.update.microsoft.com/Search.aspx?q=Windows%207%20x64%20KB2685813 and install it manually. If it tells you that it's already installed, try uninstalling it. Make sure that you reboot the VM after installing/uninstalling the Hotfix, then try to install the Horizon Agent again.
André
