"App not installed" when trying to install APK I'm trying to install an apk file on my device, and I'm able to press the Install button, but after a few seconds, I keep receiving this error: 


  App not installed. 


What is the root cause of this issue and how can I fix it?

I know this StackOverflow question is related, but that question deals more with the development aspect than the consumer installation aspect of the error.
I figured it out myself. The issue was that I had another version of the same application I was trying to install already on my device. After deleting it, the installation worked fine.