Just burned a DVD multi-session using 417 Alpha.
Sequence of events:
What has happened, is that in burning the saved session to DVD the Puppy boot files have been wiped/overwritten, leaving only multi-session stuff on the DVD - hence no boot.1. DVD muti-session burned OK using Pburn in 416 Alpha
2. Booted OK from multisession DVD uding puppy pfix=ram
3. Added some test files to root and then saved the session
4. Session seemed to burn OK this time with no Rockridge error
5. Then tried to boot the saved multisession DVD
6. Reboot then froze with message that it couldn't find the ppup-471.sfs file
So, the multi-session burn did work this time round, but there is something amiss now with how the burn is configured. So getting there but not quite there yet.
Will burn a CD multisession now and see if that works. Will get back later.