It seems that in this version I can't impregnate a slave, no matter how much I tried. I don't know if its related to the Demon race. I don't get any error on the log.
Viewing post in Aric's Expansion Rebred
There were a lot of changes to fertility in deviates code that I hadn’t noticed that heavily penalize non-standard races on top of the long ovulation timers. I am working to correct those ASAP though and will release a new version with those modifications heavily reworked to keep from penalizing any non-standard race playthrough soon.