Hello Henk,
I am sorry about the issue.
how did you attempt to delete the old backups, and is the error in the screenshot the one you had when trying this, or an error that appeared when trying to open a project instead?
Thank you.

To delete the file I've used the cross in the top of the layout and yes that's the pop ut I've sended

Hello Henk,
what folder do you see here?

To delete the file I've used the cross in the top of the layout and yes that's the pop ut I've sended

Yes on that folder

C:\Users\Eigenaar\OneDrive\Documenten\Incomedia\WebSite X5 - Pro\

Can you please access that folder in the file browser of your computer?
Does it contain folders matching the projects that you would like to delete?

Yes I've found them Thanks

Hello,
you can go ahead and delete them directly in the folder, when you next open the software they should no longer be displayed in the list.