After some forum digging i just found 2 reason for that error
1. Mismatch signature of the apk (it's only concern app update soo that's not the problem)
2. The apk that just don't support older or newer Android version ( it's that one then )
I'm not a dev or some thing like that but i like to learn and i found this
You would need to configure the android:minSdkVersion in the manifest, as explained in the documentation. This will mean that only the API methods and classes supported by the minimum SDK will be available to you. If you want to be able to run your app on different API-levels, Android market supports multiple APKs.
I read that android studio could help with that but i never done apk or code before sorry i can't help there...