Cannot complete the install because one or more required items could not be found

I tried to install Android SDK and Eclipse Galileo on a fresh ubuntu 9.10 and found the error while installing ADT Plugin for Eclipse:

Cannot complete the install because one or more required items could not be found.
Software being installed: Android Development Tools 0.9.4.v200910220141-17704 (com.android.ide.eclipse.adt.feature.group 0.9.4.v200910220141-17704)
Missing requirement: Android Development Tools 0.9.4.v200910220141-17704 (com.android.ide.eclipse.adt.feature.group 0.9.4.v200910220141-17704) requires 'org.eclipse.wst.xml.core 0.0.0' but it could not be found

It's because there are some components missed in the setup, and the Galileo update site is not in the list of Available Software Sites.

To solve the problem:
Add "http://download.eclipse.org/releases/galileo" in the Available Software Sites.

Tip: Installed Application Not Installed Error

Have you ever loaded up an application, ready to debug, but then seen a message along the lines of, "Application Not Installed" display? This usually has an accompanying LogCat error:

ActivityManager: java.lang.SecurityException: Permission Denial: starting Intent

The cause and solution are very simple:

    This error is most likely caused by a duplicate Activity class entry in the manifest file.

 <activity 
   android:name=".MainActivity" 
   android:label="@string/app_name"> 
   <intent-filter> 
     <action 
       android:name="android.intent.action.MAIN" /> 
     <category 
       android:name="android.intent.category.LAUNCHER" /> 
   </intent-filter> 
 </activity> 
 <!-- lots of stuff --> 
 <activity 
   android:name="MainActivity"></activity> 

The solution should be clear by now:

    Remove the duplicate tag from the AndroidManifest.xml file
    Build the application again
    Reload the application

This is quite the opposite of forgetting to add an Activity class to the manifest file. And, yet, it leads to a failure just the same. Proper maintenance of the manifest file is important. It's not a file to mess around with.

Happy Android Coding!