Q: INSTALL_FAILED_OLDER_SDK in the context of a virtual device, which I don't even use I have already downloaded all the SDK for everything from Android 2.2(API 8) to the latest Android 5.0.1(API 21), and have everything except television and wearable support.  My tools are from SDK 17...24.0.2.
It seems everything is ok, but when I try to test with my tablet, I get the "Failure [INSTALL_FAILED_OLDER_SDK]" error.  
To be clear, when I use Design tab in my layout (activity_new_song.xml) the virtual tablet in the Design tab shows fine and allows me to use a Nexus 10 virtual device.
Possibly, the SDK or versions are causing a problem that I cannot get the gradle to complile and run the physical hardware, a Samsung 10.1 tablet.
I know there are hundreds of these theads about this error, but I've been trying them for a week, and I'm worn down from it.  Any suggestions would be appreciated. 
Here is my activity_new_song.xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="10dp"
    android:paddingBottom="10dp"
    tools:context="com.edsets.gigmaster.NewSong">

    <!-- This is the title "Song Name" -->
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="@string/new_song_name"
        android:id="@+id/textView3"

        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:textSize="25sp"
        android:textColor="#0000FF"
        android:textStyle="bold"/>

    <!-- The user types in the song name -->
    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/editText"
        android:layout_alignTop="@+id/textView3"
        android:layout_toRightOf="@+id/textView3"
        android:layout_toEndOf="@+id/textView3"
        android:layout_marginLeft="29dp"
        android:layout_marginStart="29dp"
        android:width="400dp"
        style="@style/Base.Widget.AppCompat.EditText"
        android:textStyle="bold"
        android:capitalize="words"
        android:editable="false"
        android:textSize="25sp"/>

    <!-- This is the grid which holds the layout elements -->

    <!-- This is the Title "Your Chords" -->
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Your Chords:"
        android:id="@+id/textView4"
        android:layout_below="@+id/editText"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="39dp"
        android:textColor="#0000FF"
        android:textStyle="bold"/>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Primary"
        android:id="@+id/textView5"
        android:layout_alignTop="@+id/textView4"
        android:layout_alignStart="@+id/spinner1"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Modifiers"
        android:id="@+id/textView6"
        android:layout_alignTop="@+id/textView7"
        android:layout_toLeftOf="@+id/textView7"
        android:layout_toStartOf="@+id/textView7"
        android:layout_marginRight="50dp"
        android:layout_marginEnd="50dp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Split Chords"
        android:id="@+id/textView7"
        android:layout_above="@+id/spinner3"
        android:layout_alignRight="@+id/editText"
        android:layout_alignEnd="@+id/editText"/>



    <Spinner
        android:layout_width="80dp"
        android:layout_height="wrap_content"
        android:id="@+id/spinner1"
        android:spinnerMode="dropdown"
        android:layout_below="@+id/textView5"
        android:layout_alignStart="@+id/editText"
        android:entries="@array/PrimaryChords"
        android:clickable="true"
        android:nestedScrollingEnabled="false"/>

    <Spinner
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:id="@+id/spinner2"
        android:spinnerMode="dropdown"
        android:entries="@array/Modifiers"
        android:layout_alignTop="@+id/spinner1"
        android:layout_alignStart="@+id/textView6"/>

    <Spinner
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:id="@+id/spinner3"
        android:layout_alignBottom="@+id/spinner2"
        android:layout_alignStart="@+id/textView7"
        android:entries="@array/SplitChords"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/textView8"
        android:layout_below="@+id/textView3"
        android:layout_alignParentEnd="true"/>

</RelativeLayout>

Here is my build.gradle:
apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"
    defaultConfig {
        applicationId "com.edsets.gigmaster"
        minSdkVersion 21
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    productFlavors {
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:21.0.3'
}

