Yes, I stupidly updated my machine when software update showed up. I normally don't do it the first day... expecting it to be recalled--hahahhaha, like it was this time.... joke on me I guess.
Anyway, I did get it to build. I moved the files to the same hard drive as FM Dev Tool, I rebooted my machine (just in case), and it worked.
If it as stupid a bug as not being on the same hard drive... well, quality assurance at FileMaker should be embarrassed.