I SOLVED THE ERROR CODE 3!!!
HOLY COW, I finally discovered the answer for the Error Code 3, guys! At least for my type of Error Code 3, where it could not open a particular file when trying to burn a blu-ray (either disc or image).
In searching for an answer, I just happened to stumble upon the Wikipedia article for Encore, which says that AVCHD 2.0 files are not compatible for burning to blu-ray disc in Encore. So I decided to go back into Premiere and re-export the timeline to MPEG-2 Blu-Ray, bring those files (m2v and wav) into Encore, and voila - it wrote the ISO, no problem!
