Got it working now, I'll soon make a new release. Just need to really make sure what the error was.
Edit: there where two errors:
1) Lightroom cannot handle FM with too high precision in the rational numbers, they use 1/10000, I have 1/1000000000 but then it goes haywire
2) Lightroom cannot handle other observer than 1931_2, DCamProf uses the more realistic 2006_10. By some (stupid) reason Lightroom makes a check that FM x 1,1,1 = D50, and D50 varies slightly depending on observer, and thus if you have not used 1931_2 it breaks.
I'll add a workaround for this and publish in an hour or so, but I can't say I think Lightroom does it the right way. There's no reason to "sanity-check" the D50 whitepoint this way, and why they can handle high precision rational numbers is a bit strange too.