jAlbum 16 is using a new project format and it automatically updates projects listed under "Recent projects" to the new format. This means that once you've moved to jAlbum 16 you cannot open such projects in jAlbum 15 and older versions. However, this tool enables this by converting back projects to the pre v16 format. Only run this tool on jAlbum versions below v16.
To install, download the attached tool and put it inside jAlbum's "tools" folder, then restart jAlbum. Now open the project that fails to load properly and execute this tool via Tools->External tools->"Convert project format to pre v16 format". Once the tool is finished, close and reopen the project (CMD/CTRL+W followed by CMD/CTRL+1)
With jAlbum 16, the control files "albumfiles.txt", "meta.properties" and "comments.properties" now resides under a hidden ".jalbum" folder in each image directory (cleaner file structure). This tool, moves these files back from the ".jalbum" folder to their original location.