I know this post is a bit old, but I came across this very same issue recently and tracked it down to a scripting issue. The reason I bring it up here is the scripting problem arose from using a change to the PlayGui.gui that originated from...dun dun dun...Richard's RTS tutorial. The culprit was removing the GuiControl(DamageHUD) from the PlayGui. Obviously there are player scripts that will be trying to alert the player they just took fall damage and use the 'DamageHUD' that is no longer there. Of course, if the goal is to ultimately remove the DamageHUD (because it does get in the way of AIPlayer click commands) then the scripts that deal with push/popping the damage direction gui elements need to be removed as well. For some reason, the scripts feel it is necessary to report to the player the damage direction they just took fall damage from...lol. Anyways, fixed an issue I was having with crashes due to player landing, cheers!