You have to rename the file extension from .bak to .dlx. After that, DIALux will recognize and open this file. If your file extension is not visible, you need to go at Start > Control Panel > Appearance and Personalization > Folder Options > View tab. Clear the Hide extensions for known file types, check box and then click OK. Go to your file, right click on it and select Rename. Delete .bak and type .dlx instead.