This is a bit mysterious. Whenever I'm running a sim with .sexrepro I get random CTDs. They don't produce error.sim to post, but instead a windows error report pops up. The pictures I've attached are screencaptures from the error report. They have the same dll file on them, ntdll.dll. I've also attached a sim that reproduces these errors quite often (the zip-file). I'm using almost exactly same settings in my other sim with no problems. The only main difference is the species that uses .sexrepro instead of .repro.
Also, I've got dual core, so I'm running two different sims at once, if that matters. The other one runs fine though (no sexrepro there).