Hello Ann,
thank you for this information. I can confirm that it works. We had a really old Delphi project which we could not scan for years (no working Delphi plugin), but we kept the project because of, well, it was nice to sometimes have a look at the issues that were found. 
After I deleted the project, the database update completed successfully.
Now I just need a solution for this to complete a first analysis with the new SonarQube version.
Thanks for your help.
Markus