Hello Henk,
is the error displayed during the attempt to delete these projects?
Could you please provide a screenshot?
Thank you.

Somethhing wrong during loading of ths project.

There are several projects I cannot delte

Hello Henk,
please check the Preferences menu of the software, and take note of the folder where projects are stored.
Close the software and to to that folder, deleting the folders corresponding to the projects you wish to delete.
Please take care not to delete folders for projects you are still using.
Once you re-open the software, they should no longer be listed.