Why does it say the file does not exist when I open my previous project?

There are two factors causing the issue: 
1. The source files (photos/audios/videos) are deleted, renamed or removed to another place. To open the project file, you need to move back the source files to the original location.

If you cannot remember the path of photos, you can open the project using a text tool to check it. Right click the project file and choose Open it as Notepad++. For example, you would find the path like this: Source Path="C:UsersPublicPicturesSample PicturesTulips.jpg" MediaStart="0" MediaStop="60000000" Seekable="1">. If you don't have a text tool available, Notepad++, which you can download from:http://notepad-plus-plus.org/, is recommended.

2. The removal of the external devices which contain the source files. You need to re-connect it well and then you will able to open the project file.

Tips: We suggest you use the backup feature to avoid this in the future. Please click the DVD Slideshow Builder Deluxe/Standard at the top left corner and then select Backup Project to backup a project. Then if some of the source files of  a slideshow are moved, deleted, or renamed, you can also open the project.