An offline file is a placeholder for a source file that Premiere Elements cannot currently find on your hard drive. Offline files remember information about the missing source files they represent. If an offline file appears in the Quick view/Expert view timeline, a “Media Offline” message appears in the monitor and in the Quick view/Expert view timeline.
If you selected more than one offline file, the Attach Which Media dialog box appears in turn for each file you selected. Pay attention to the offline filename in the title bar of the dialog box so that you relink the correct source file to each offline file.