I have to think the block you commented out is probably a red herring, unless there's some kind of interesting output being done in Mob_DisplayDate(). It's more likely the issue is connected to some kind of savefile corruption that may have occurred at one point--although I hope not, because presently I have no hope of finding such an issue.
If uncommenting that block does cause crashes to recur though, that's a good place to zero in on.
1. Cleaned up the world.sav file by removing users who haven't logged in 90 days. It removed about 300.
2. I commented this block from my world tick. I will be uncommenting this as my next step. I will wait until Sunday or so because I want to make sure the crash is gone.
for (var/mob/m){
if (m.client)
{
m.Mob_DisplayDate();
}
}