Thank you for the indications.
Finally, I succeeded in recovering the charts on the PC Panasonic CF-33 which I use for my navigations, and that it is essential.
On the other hand, on the test PC that I have at home (PcDellHome), I did not succeed in restarting the charts: they exist, they weigh >1Go but OCN, even after a restart, does not succeed in loading them.
But that's not dramatic, the main thing is that I was able to recover my charts on the PC dedicated to
navigation.