Missing required part when exporting solution

Hi Everyone….

I am customizing  CRM 2013 and when I try to export my solution it shows warning message that

 "The following components are missing from your solution. Import will fail if these components don't exist already in the target Microsoft Dynamics CRM Organization. To add the missing components to your solution, cancel the import open the solution and click the add required button."

 and my missing component is:

I tried to look to add those in to my solution as message says but I can't find Sales attachment from the list.

Reason why I am exporting is to edit sitemap. So what I understood is that I should export my solution and use XRMtoolbox site map editor to customize navigation bar and import it back, is it right?

I am totally new in CRM and I am really stuck with this problem on exporting and editing sitemap.

Please advise my how to solve

Thanks in advance.