Robert,
Thank you very much for your help.
I commented ou the first, then the second, then both and nothing, still the same error.
I took a look at the widgets in the UI elements, and one by one, I saw it seems to be the HeaderController widget that causes the bug : with this one commented out I don't have the error and it opens.
But I have a big white banner instead of where should be the title, icones of widgets, etc.
I put the original code in my HeaderControllerWidget.xml but then the error is back and nothing opens except the splash window and the basemaps buttons.
Any idea??? 🙂
Anne-Laure