Question about Chain Spell

[Illithilich]

I want to use the Chain Spell metamagic feat on the Darkbolt spell (pg. 210 LoM or pg. 90 BoVD). Darkbolt does damage normally, but has a side effect of stunning the target for 1 round if they fail a fortitude save. My question is, if I apply chain spell to it, is the secondary stun effect at -4 DC because of it, or does it stay the same (if feel like it takes a penalty, but it says that spells that do no damage take the penalty).

[Biffoniacus_Furiou]

Chain Spell only applies a -4 to the secondary target DCs if the spell can't deal damage. Secondary targets will take half damage from the spell, but they'll have to save at the full DC or be stunned.

[Keld Denar]

Note that Darkbolt was reprinted in the SpC. Being that the SpC is the most recent of those sources, it functions as errata. The new Darkbolt is still really cool, but its also 5th level and doesn't really chain that well.