Hmm, that's interesting. I did in fact make a disc image, as I always do that so I can make future copies of the disc easily in the future, and I hate having failures while burning to disc. It would be a hassle to have to re-encode the videos each time, but if the disc worked, it'd be worth it. Of course, then I'd have to store the movies somewhere if I ever wanted to make another copy. They're ProRes files, and they total about 1.5 hours, so that's a lot of disk space, which is another reason I like to save disc images instead. Oh well, like I said, it'd be worth it if it worked! Weird that Toast would behave that way. I used my last blank Blu-ray disc, so I'll have to order some more and try it this way.
Thanks for the tip! I'll let you know if this works for me.
PS - What do you think would happen if you created a disc image from one of your successfully created Blu-ray discs? Would Toast then be able to make a working copy from that, do you think? Have you tried that?