Android Studio generated APK installs in debug but not release

I have written a small app in Android Studio which is targeted for API 23 (6.0 Marshmallow) which is what is on my phone. It installs and runs perfectly in debug mode but when I have Android Studio generate a signed APK, the signed APK does not install and has either "App not installed" or "There was a problem parsing the package." I have tried every trick I can find online to no avail. The phone is set to install from unknown sources; the targeted API is what is installed on my phone; and I have not renamed the package. I get the same results from APKInstaller, AndExplorer and just tapping the package in File Manager. Also, I get the same results when the apk is on the SD or internal storage.
I would greatly appreciate help on this problem.
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Jackie ManCommented:
Give details on how you generate a signed APK.

Have you tried to install the .apk file in another android device?

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rkulpAuthor Commented:

Thanks for your reply and link. I was using the "Generate Signed APK" using my existing keystore. When doing that, it shows the passwords as dots and I assumed that meant they were remembered which is common in some programs. I expect they were not. I then used the automatic generation of the signed APK which I found in the link. I had to manually put in the passwords. It worked fine this time. Thanks for your excellent help.
rkulpAuthor Commented:
Thanks very much.
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