It may be lucky your attempt failed, though: Blizzard tells Shacknews it's working on a "pseudo-LAN" solution to the problem, that might allow play very similar to a regular LAN party, with Battle.net only being pinged once or periodically for authentication purposes.
Even better, Shacknews also reports that a similar system will be included with Diablo III. While it's not quite offline play, we're hoping it's close enough to keep both developers and fans happy.
