Problems with an old Brazil/Bongo animation

I was asked to see about re-rendering an old Bongo/Brazil animation from 2011, and it’s not really working. I’ve tried V5 and V6 and rendering seems to be stuck on the Global Prepass step of the photon map…or at least it takes an insane amount of time, I’ll give it a few more minutes to test. Along with that I get an odd message in the V5 command line, “Unable to open bitmap file - unknown file typeUnable to open bitmap file - unknown file type.” Where the heck do I even begin to figure out what the problem might be?