I tried to download Horizon and it said that it was not compatible with my PC, I am operation on Windows 8.1 and it said to ask for the correct app version.
https://www.horizonmb.com/client/v2/Horizon.Setup.v2.8.0.1.exe try downloading it from that link instead.
My Horizon is offline! Help 
I try to remove firewall but nothing … So I do not have access to the functionality of Horizon and wanting to throw horizon, it also puts me to download Diamond Tools, off when I run the setup , an error message appears: “The setup files are corrupted Please obtain infor- a new copy of the program.” Thank you
Delete the “Daring Development” folder in your Program Files (x86) located in your OS.
it still says “The setup files are corrupted Please obtain a new copy of the program.” for me
Delete any Horizon installers you might have downloaded on you PC and then try Downloading and installing from this link Horizon 2.8.1.1