Manifest Error App Crashes

Manifest Error App Crashes

I reinstalled Windows on my pc and tried to open my old project with a
newer version of android studio.
This is my Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.linkr.chat"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:label="@string/app_name"
android:name=".Login" >
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
When i change the line android:name=".Login" to android:name=".Chat", the
activity Chat opens up and doesn't crash. But i want Login to open first,
so i use android:name=".Login", and if i then click on the button to open
the chat it crashes.
The error i got from logcat was:
Caused by: android.content.ActivityNotFoundException: Unable to find
explicit activity class {com.linkr.chat/com.linkr.chat.Chat}; have you
declared this activity in your AndroidManifest.xml?
Why does it want me to declare this?
Thanks a lot!