I assume you mean that when you open the project you get the error message?

Open WX5, highlight your project and select backup.

If there are any saved backups you can select one and Redo to (hopefully) restore your project.

If there are no backups, have you ever exported the site (step 5, export project to create an iwzip file)? If you have done so you can open WX5, select import, browse to where you stored the iwzip file and restore your project (this will NOT overwrite the existing project).

Please be aware that an iwzip file is a complete backup including source materials, unlike the built in backup it will enable you to restore the project to any PC. When working, please export your project regularly, they can be renamed (perhaps with date?) as required so you can have many fall back options.

Morning,
I've never made any backup.So what now ?

When you open wx5, select project then select backup, if there are no backups available you may have no choice but to recreate the project. If the website is online you may be able to save significant work using copy and paste to create a new project.