I'd like to add a hint to help you help yourself on future occasions. There are multiple search functions in the CS: the most handy one for this task is "Edit->Find Text". If you'd like to find all instances where Dagoth Gares is referenced, determine his ID (dagoth gares), and enter it as the search text. Click on "Find Text", and the Text Search window will display all dialogue lines, scripts, and objects in which that ID is used.
This is from the uesp: Disable/Enable: Used to enable/disable objects within the game. A disabled object is saved but not visible or processed within the game (though any scripts attached to it will still work). Note that it is dangerous to disable an object within its own script (causes crashes).
I disagree with the UESP here. I've been enabling/disabling references from their own local scripts for years now and have never experienced crashes from it. I suspect that the UESP meant that "it is dangerous to remove a reference from the gameworld by its own script (SetDelete). Like NMZmaster said:
[...] In a similar vein, I have had crashes where I didn't wait long enough between Disable and SetDelete-ing an object, but never with Disable by itself.
This is a well known problem, documented for example in http://planetelderscrolls.gamespy.com/View.php?id=6083&view=Mods.Detail:
Notes and cautions:
SetDelete will crash Morrowind if there is any other function operating on the object in the same frame. It will also crash if the object emits sounds (or plays animations with linked sounds) and is disabled and deleted in the same frame (forum info / JOG).
In the following paragraphs, MWSFD provides several solutions to the problem.