Crashes

Common problems that may cause crashes in-game.

Deleted References

If you delete any vanilla (Oblivion.esm) refs and another mod loads after yours that does anything with those refs that you deleted, the player will very likely get a crash on exit and/or a crash when reloading with a savegame made in another cell than the one he's currently in.

The solution is to never delete any vanilla (Oblivion.esm) refs. Move them and/or set them to be Initially Disabled instead. Shoving an object out of view by +/-150,000 Z units (arbitrary value) will put it far enough away that the game won't render it anyway. The drawback to this is it may generate CS warnings about potentially invalid Z values.

See here, here, and here for more details.

Nested If Versus And

Don't assume that if-tests stop at the first non hit. For example,

 if (myref.isactor and myref.isincombat)

could cause a crash because myref.isincombat is always checked, even if myref isn't an actor. Use a nested IF statement instead.

Existing Object Names as Variable Names

Don't use existing object names as variable names. The existing ones get priority. If you write:

 ref bed
 set bed to ThisBedref
 player.moveto bed

this will probably cause a CTD because 'bed' is also a topic id and will get priority here.

Other possible mistake names: enemy, accept, contract, creatures, gift, help, inventory, positions, placeholder, tasks, themage.

Quest Targets

Deleting a quest target will crash the CS. You can get around this by setting the conditions so that it's never displayed.

Referencing Deleted Objects

It's easy to cause a crash by using a reference to an object that was deleted, or, in some cases to a dead actor.

For example, when using GetSelf in ScriptEffectUpdate or ScriptEffectFinish blocks for area of effect scripted spells, GetSelf can point to a dead body

This will cause a crash if you try a function that requires the object to be an actor, or even null if a summoned creature has been killed in the area.

Bow Reach Bug

This bug is fairly well-known but still crops up on occasion. The game will CTD if a bow with Reach = 0 is equipped by anyone (player or NPC). Some of the vanilla Oblivion bows have this problem, so be sure not to replicate the error in your mod.

SetLevel Bow Bug

Strangely this bug is mostly unknown (and the Bow Reach doesn't have to be zero to produce a CTD). It causes almost always a CTD if the player uses SetLevel on an actor that has a bow equipped or drawn and is inside the players cell (the CTD occurs as soon as the player visits or is in the cell where the actor was forced to reequip his bow due to SetLevel).

To avoid the CTD the actor has to be moved to a never-to-be-visited-cell to do SetLevel and then move the actor back to its origin. That can be done in a single frame.

Activate Self

When you script an object

1. to Activate itself
2. from a block that continously runs (i.e., GameMode, MenuMode, etc.)
3. and not bypass the OnActivate block, as such:

begin GameMode
Activate player, 1
end

begin onActivate
...

you can cause an CTD. It seems that self-activation causes the entire script to run from the top, including the GameMode block, and so will Activate itself infinitely. You can prevent this by placing the OnActivate block before the self-activation, as such:

begin onActive
...
end

begin GameMode
Activate player, 1
end

Activating a Container (including NPC)

If you meet all of these conditions:

1. Activate a Container, so that you run it's OnActivate block, that is:

YourContainer.Activate player, 1

1. from an Object Script (and maybe a Magic Effect Script, but a Quest Script, direct activation, or dialog script would be safe)
2. when a scripted item is in it (even a Scriptname declaration is too much)

you will get a CTD upon activation. The easiest way around it is to place the script on another object (an Activator, etc.) and activate it instead of the container. You can also use a Quest Script to activate the container, as such:

scn YourOpenerQuest

ref   rContainerToOpen
float fQuestDelayTime

begin GameMode
  if (fQuestDelayTime != .01) ;to activate the container quicker
    set fQuestDelayTime to .01
  endif
  rContainerToOpen.Activate player, 1
  StopQuest YourOpenerQuest
end

and use this whenever you want to activate a container:

scn ActivatingScript
set YourOpenerQuest.rContainerToOpen to YourContainer
StartQuest YourOpenQuest

MessageBox on a Terminating Script

You will very likely get a CTD if you open a MessageBox just before a script terminates. For example, if you have some scripted condition on an item that will force the player to drop the item, don't use a MessageBox in that condition.

 scn MyItemScript
 begin gamemode
  If PCVampire
   MessageBox "You can't use this item while you're a vampire."
   Player.UnEquip MyItem
   Player.Drop MyItem 1
  EndIf
 end

It seems that the script terminates after the drop (because it's attached to MyItem), but the MessageBox is still active so you get a CTD.

You can avoid this particular case by using Message instead of MessageBox:

 If PCVampire
   Message "You can't use this item while you're a vampire."
   Player.UnEquip MyItem
   Player.Drop MyItem 1
 EndIf

Which doesn't cause a CTD.

Edits to Tamriel cell (-47,-7)

Any change to Tamriel cell AnvilMainEntrance (-47,-7) will not cause crashes in-game, but instead will cause Oblivion to crash on exit from the main menu. There may be other cells that also do this. The presence of the CELL record is enough; even if all the refs. are removed the crash will still occur if the CELL record is still present.