OK, a new fix, although a very risky one, found by searching from the error you provided, Saint Gregory. It turns out I am right and Preloader wants to use the real IOS36 and won't use IOS249. However, you can use one of the apps that actually replaces IOS36 with a vulnerable one.
Info here.
So it turns out that cioscorp is what you need, or just to use the WAD installer you used earlier to install cIOS36.wad from cioscorp.
I'm also looking to see if there's a Preloader installer that uses IOS249 instead, but that's not showing any results so far.