Why wont an app install

[AC Question]

When i click on a youtube link (actually i have clicked on 4 or 5 links and its still doesnt work) and when i tap download it will download then i press install and it will say app not installed and i've checked if the file was corrupt or damaged but its perfectly fine.

 

[Raptor007]

Are you trying to d/l apps from YouTube or links offered within YouTube? It could be you do not have security turned off to allow installing apps from unknown sources. Its under security.