After hours and hours of internal software errors that drove me mad, I found a solution for my problem. If you’ve got subtitles in your project, this might help.
I’d already made a DVD project in PAL and successfully built an image of the disc. I then made another project for an NTSC version and used Aegisub and Subtitle Edit to help me convert the speed of all my subtitles. The subtitles came into the NTSC project without a hitch, but every time I’d go to build, Encore would throw those PGC internal software errors at me.
After trying logical solutions, then even the crazier ones like manually typing out my subtitles again (just a bit to test…wasn’t that crazy), I used Subtitle Edit to shorten the durations of every subtitle (increasing the gaps between them slightly) … and it worked.