Android – Installation failed because APK was not signed

I just upgraded Android studio from 1.5 to 2.2, and now there is an error running my app:

I have used Google to search, but it doesn't help me. My gradle file is:

...
android {
    signingConfigs {
        myapp_signed {
            keyAlias 'mkey'
            keyPassword 'pwd'
            storeFile file('.../_keystore.jks')
            storePassword 'pwd'
        }
    }
    compileSdkVersion 22
    buildToolsVersion "21.1.2"
    defaultConfig {
        applicationId '...'
        minSdkVersion 14
        targetSdkVersion 22
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
            signingConfig signingConfigs.myapp_signed
        }
    }
    productFlavors {
    }
}
...

Does anyone know how to solve this problem? Before I received this error, I encountered another error, which said:

I solved the "gradle version 2.10 is required." error like this

Edit: even if I switch the build variant back to debug mode, please uninstall the application and try again. I will get the same error

resolvent:

For me, the solution is to update all the libraries I use and update them to Android 23. Maybe it helps someone