I have a program working in the Android Emulator. Every now and again I have been creating a signed .apk and exporting it to my HTC Desire to test. It has all been fine.
I only encountered the App not installed
error when trying to install an apk on my phone which runs on 4.4.2 aka KitKat, but my friend did not encounter this error on his phone which runs on 6+. I tried the other solutions such as removing the old/debug version of the app because the apk was a release version, clearing the debug app's data, and even clearing all of my cached data. Then, finally I realized all I had to do was select both signature versions when building my signed apk.
Before I only had V2 (Full APK Signature)
selected, but after selecting V1 Jar Signature
as well, I was able to successfully install my signed APK on my 4.4.2 device. Hope this helps others!
My problem was: I used the Debug Apk, that was generated while I did the Run command from Android Studio
Solution was: Instead of using this file, clean project and click Build > Build APK(s) from Android Studio. Then you can use the generated APK from the usual folder (app/build/outputs/apk/debug/)
The file that was generated like this installed without a problem.
In the end I found out that no apps were being installed successfully, not just mine. I set the Install App default from SD card to Automatic. That fixed it.
I faced with the same problem. The problem was the main activity in my AndroidManifest.xml file was written twice. I deleted the duplicate.
Check with the Android version.
If you are installing non-market apps, and incompatible version you will get this error.
Ex: Application targetted to 2.3.4 Your device is 2.2 Then you will get this error.
Apparently this can also be caused by renaming the APK prior to installing it. I wanted to reduce the amount of typing users had to do to get the app from our web site by shortening the file name. After that, they were unable to install it.
Once I reverted to the original file name used when creating and signing the package I was able to update the installed app.