I'm not sure how many folk on here use the Dark Reign forum but this has been a recent topic of discussion.
In the rules it states that Dual Strike cannot be combined with Lightening Attack but does not say it cannot be combined with Lightening Attack's prequisite, Swift Attack. This point has been argued by several people, stating it should be legal. I agree it is strange to say it cannot be used with one, but not the other.
The other view (the view I have argued), is that the descriptions of both Dual Strike and Swift Attack state "as a full action". Since a character can only make 1 full action or 2 half actions in a single round of combat, they cannot be combined.
This has not been cleared up in any of the Errata.