Thanks Marco. That was actually the cause of the crash !
I do not know why it affected only these 3 notebooks and not all the others I have. But using your hint, I opened each notebook again in V9, changed the style sheet to something else, I picked report
style. Closed all notebooks. Opened them all now in V10, and there was no crash anymore.
Then in V10 changed the style sheet back from report
to default
. Closed them. Now they all open fine in V10. The stylesheet setting is now fixed inside the notebook.
Why would V10 be looking for a style sheet in the V9 folder any way? Strange. But the problem is fixed now.
Thanks for your help and trying them.