SVN version 18138 is one of the most stable SVN builds I've seen in some time, if it wasn't for this one bug I'd package another windows beta installer.
This occured after starting a new game, shooting down one UFO, completing the ground mission and storing the UFO in the base, then advancing time on the geoscape. I built two radar towers after storing the UFO and all aircraft were back in the home base. When advancing time for the next mission, it didn't crash right away, the Sun and Moon spun around several times before the game crashed, I'm guessing it couldn't set up the next mission properly and this is what stopped everything.
The assertation failure occured in cl_aliencont.c, sorry I don't have a screenshot.
I also noticed in this version the battlescape with the skirmish mode was very slow, very low framerate, but this problem did not exist when playing the ground mission in the standard campaign.
