How to fix Activitynotfoundexception error?

Question

I have two activities put in extremely different packages as shown in the codes below:

Mainactivity

package com.main.package;

import ...;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Intent i = new Intent(getApplicationContext() ,OtherActivity.class);
        startActivity(i);
    }
}

Otheractivity

package additional.package;

import ...;

public class OtherActivity extends Activity {
    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    Intent i = getIntent();
        if (i != null) {
        String errorMessage = i.getStringExtra("error");
        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        dialog.setTitle("A error was found!!");
        dialog.setMessage(errorMessage);
            dialog.create().show();
        }
    }
}

Androidmanifest

<activity
    android:name=".MainActivity"
    android:label="@string/app_name"
    android:screenOrientation="landscape"
    android:theme="@style/Fullscreen" >
    <intent-filter>
       <action 
          android:name="android.intent.action.MAIN" />
       <category
          android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
 </activity>
 <ativity
    android:name="additional.package.OtherActivity" />

But I’m always receiving the Activitynotfoundexception exception even though Activity is set on Androidmanifest.

Error

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.main.package/com.main.package.MainActivity}: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.main.package/additional.package.OtherActivity}; have you declared this activity in your AndroidManifest.xml?

How can I fix this error? This is happening because of the packages?