Starting for the first time a big database imported from a dump, I got an error that I can not close.
Remark: it turned out that I was trying to import a v3.5 dump in a v4.2 graph.
So it is okay to get an error, but the behaviour of Desktop is suboptimal...
Remark about the import: it is weird that the dump was imported without an error by 4.2 but the graph could not be started...