Both Mac platforms tested and failed (PPC & MacIntels) running 10.5 with only standard Quicktime plugin's plus the ones installed from Toast.
All versions of Toast 7.0 - 7.1.2 produce the same error message BEFORE attempting to burn any video, audio or disk images on MacIntels.
On PowerPC Mac's I get the same error message too but sometimes the program just crashes without any error message or error in console's log.
And yes I have seen the first post about an update coming for 10.5 users.
Unfortunately for the 200+ clients that decided to take the leap to 10.5 , it's been a technical (software updates) nightmare trying to keep their productivity alive.
Toast 8 was no solution either since it produced the "Result Code: -13780" error at the end of every burn for them.
So for the sake of all Apple technicians on the planet, please hurry with the patches to Toast 7 & 8!