Thanks for your reply tsantee.
Well what I did is this : I cleared all Roxio files and apps from my internal HD, emptied the trash (the only files I did not delete were Roxio files in the System/Library/Frameworks, I don't want to mess with that at all). I reinstalled from scratch from my Roxio install disk (10.0.4).
I did have a backup copy of the older version (10.0.8) on an external HD so I swapped the Toast app with the one from the external HD. I was able to burn one DVD and when I tried to burn a second one (I have too many photos to backup LOL) it did the same thing again ! Same error message and it refuses to burn any DVD, no matter which brand I try. Trashing pref files won't even allow me burn another DVD now. *Sigh*
So now, I cleared everything Roxio and/or Toast from my internal HD and am burning through OS X's Finder. I've given up, I've tried everything I could come up with as a possible solution. I guess there's a hidden file somewhere that's now corrupted and makes Toast Titanium go berserk.
I'll try to keep up to date on replies in this thread, see if there is a patch to this patch to fix things. If not, Toast is toast for me right now I just don't have the budget to go to Toast 11 presently. And I'd have to see if requirements for Toast 11 accept Mac OS X 10.6.8.
Thanks again for your reply tsantee and have a great day !