Signature Error on Install app-release.apk

[ac4android]

I want to re-install version 1 of an app after some minor modifications.
The original app-release.apk installed nicely with the .keystore that I generated for it.
I took note of the password, the key-password and the alias
After the modifications, I recompiled but left it at version1.
Using the same .keystore, password, key-password and key alias, I generated the app-release.apk
I tried to install the new .apk but got a "signature error"

QUESTION: how do I re-install the new .apk and why do I get a signature error?

 

[Deleted User]

Well that's a strange error, but I'm pretty sure you're not allowed to re-release an APK with the same version number. It's got to be increased.