containers naviguation buttons: exception when switching from a read only container to an updatable container

60 r23251

I have three pages in my top menu: the first two ones have been notified, and so are locked. So I access it in read only mode. When I switch to next/previous ctn, no problem between the first two ones
I get the attached exception when I switch from a ctn in read only mode to the editable one.
No pb when I edit directly this last one
No pb from editable to read only