Project 'MyApp' is missing required Java project: 'google-play-services_lib'

Question

I got an app from internet and I want to run it on my eclipse emulator. but after I imported, it had a problem on error log said : Project 'MobileAssistant' is missing required Java project:'google-play-services_lib'.

I've looking for the solution and I got : Import google service form Project -> Properties -> Android -> Add google play but I couldn't add it coz it had a cross sign on it.

here the android manifest :

    <?xml version="1.0" encoding="utf-8" standalone="no"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.google.sample.mobileassistant"
    android:versionCode="2"
    android:versionName="2.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="16" />

    <permission
        android:name="com.google.sample.mobileassistant.permission.C2D_MESSAGE"
        android:protectionLevel="signature" />

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="com.google.sample.mobileassistant.permission.C2D_MESSAGE" />
    <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="android.permission.GET_ACCOUNTS" />
    <uses-permission android:name="android.permission.USE_CREDENTIALS" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.google.sample.mobileassistant.SignInActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name="com.google.sample.mobileassistant.MainActivity" >
        </activity>
        <activity android:name="com.google.sample.mobileassistant.PlaceDetailsActivity" >
        </activity>

        <service android:name=".GCMIntentService" />

        <receiver
            android:name="com.google.android.gcm.GCMBroadcastReceiver"
            android:permission="com.google.android.c2dm.permission.SEND" >
            <intent-filter>
                <action android:name="com.google.android.c2dm.intent.RECEIVE" />

                <category android:name="com.google.sample.mobileassistant" />
            </intent-filter>
            <intent-filter>
                <action android:name="com.google.android.c2dm.intent.REGISTRATION" />

                <category android:name="com.google.sample.mobileassistant" />
            </intent-filter>
        </receiver>
    </application>

</manifest>

pleaze help me, how can I solve this and what cause it?

tq be4...