Add button to Ribbon but they don't show up?

Question

Here is the xml from element file. It's scope to web.

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <CustomAction Id="HelloWorld"
                Title="Hello World"
                Location="CommandUI.Ribbon"
                RegistrationType="List"
                RegistrationId="101">
    <CommandUIExtension>
      <CommandUIDefinitions>
        <CommandUIDefinition Location="Ribbon.Documents.Manage.Controls._children">
          <Button Id="Ribbon.HelloWorld"
                  TemplateAlias="o1"
                  Command="HelloWorld"
                  LabelText="Hello world"/>
        </CommandUIDefinition>
      </CommandUIDefinitions>
      <CommandUIHandlers>
        <CommandUIHandler Command="HelloWorld"
                          CommandAction="javascript:alert('Hello world from ribbon !');" />
      </CommandUIHandlers>
    </CommandUIExtension>
  </CustomAction>
</Elements>

Answer 1

The following is the corrected code and is working now. Make sure to copy the image "copy_item.png" (http://www.iconfinder.com/icondetails/11062/32/copy_document_icon) to images folder (under 14 hive).

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <CustomAction
   Id="CustomRibbon"
   Location="CommandUI.Ribbon"
   RegistrationId="101"
   RegistrationType="List"
   Title="Copy Item to Doc Lib">
    <CommandUIExtension>
      <CommandUIDefinitions>
        <CommandUIDefinition
         Location="Ribbon.Documents.Manage.Controls._children">
          <Button
           Id="Ribbon.Items.Manage.CustomRibbon"           
           Command="CopyItem"
           Image32by32="/_layouts/images/copy_item.png"
           LabelText="Copy Item"
           TemplateAlias="o1" />
        </CommandUIDefinition>
      </CommandUIDefinitions>
      <CommandUIHandlers>
        <CommandUIHandler Command="CopyItem" CommandAction="javascript:alert('Hello world!');" />
      </CommandUIHandlers>
    </CommandUIExtension>
  </CustomAction>
</Elements>

Answer 2

The code provided works fine on my machine.

1. Double check that the feature is activated on the web
2. The button (as currently defined) will show up only on the list view page of a standard document library