If the original project can no longer be loaded, the backup file can be used under certain circumstances. Backup files are generated automatically by DIALux every time when saving. 

A backup file is created automatically each time you save your project file. This file has the same project name and is located in the same folder as your actual project file, but has the additional extension ".bak" ("project name.evo.bak").

You can convert this backup file back into an evo project file yourself by deleting the ".bak" extension and giving the project file a different name ("Project name.evo.bak" => "Project name 1.evo").

After renaming it, the file should be readable as every other DIALux project file.