Hi
As noted above, the vpj file is NOT a video file or a video clip. It is a text file containing information about your project.
In short you open VP and add clips/audio/images etc. You can then place these clips on the timeline and edit them, add effects/transitions/texts and titles etc. This is your project.
At some point you may wish to save your work. You do this by invoking the option Save Project. This command will make VP create a vpj file. This file holds the list of clips you have used, their location on your PC and the editing steps you have made to create your project. It is a data file in text format. Using Save Project will overwrite any previous vpj file you made with this command.
If you want to save your project at different points of development use the option Save Project File As. This enables you to enter a specific name and destination and will not overwrite previous vpj files.
VPJ files are not video clips and are designed to be opened by VP. If their icon is double clicked VP will open, read the file, load the clips from their recorded location and assemble the project to the state it was when the project was saved.
Normally this is done quite rapidly as copies of clips and thumbnails are stored in the cache file and can be retrieved fairly quickly. However if the cache has been emptied in the interim, VP has to retrieve the clips from the actual pc locations and this can take much longer since the cache also has to be reloaded. If, as can happen you have moved/deleted or renamed any of the clips/images etc. VP cannot cannot find and load them but it will list the missing items and prompt you to locate them.
Saving you project as a playable video is referred to as Exporting the project. There are numerous options when doing this but the end result is a Video clip.
Don't get mixed up between the vpj file and the exported project.
Are you saying that VP will not open your vpj file?
Nat