I did, or I think I did, it did not solve anything because it also couldn't get exclusive access to /var/lib/dpkg... I have been able to complete the restore with the vanilla kernel. Since my Nokia store apps are currently lost, I'm going through Warehouse reinstalling all that are available, before doing a new restore point, disabling the security code (that open-mode kernel does not support) and then trying again. But that's not going to be any time soon, maybe next weekend.

So, the easiest way is to read everything as I've read,
Do a backup from inside the phone,
mount MyDocs as mass storage,
copy everything out especially the .backups folder,
flash,
connect to the network,
install n9repomirror and developer (phone will restart),
install warehouse,
mount MyDocs again, copy back the .backups folder, unmount MyDocs,
go to Settings/Sync and Backup (I think)/backup, select the last restore, restore, and wait for a restart.
After the restart, the App Manager will ask if you want to restore your applications, unfortunately you can only restore one by one...