Among those thwarted that day was Chris Nowaczyk, a cancer researcher at the University of Pennsylvania. He had gotten in but was in the middle of registering when the system crashed.
Nowaczyk was peeved.
So he decided to organize his own event, Dîner en Noir. He found like-minded people to help.
"This was born out of frustration," Nowaczyk said. "It was a spur of the moment thing. I felt excluded."
On the evening of Aug. 21, just as 3,500 people dressed in white will attend the sold-out Dîner en Blanc at an undisclosed location, Nowaczyk and his crew plan to host 500 people dressed in black - with a splash of red (this year's color) - at Dîner en Noir, also at an undisclosed location.
(Wouldn't it be a knee-slapper if both groups go to the same location?)
Dîner en Blanc Philadelphia co-founder Natanya DiBona called the situation "unfortunate."
She said she was logged into the system on July 17, watching in vain as the registration attempts by Nowaczyk and several others were disabled by the system. She said that she tried to assure them that their registrations were valid, but that they did not want to hear it.
Within hours, Nowaczyk and allies had registered phillydinerennoir.com and had set up a Facebook page, proclaiming a "revolution."
He also enlisted the DJ services of Robert Drake of WXPN.
The rhetoric seems to be less strident now as Noir closes in on its target of 250 tables for two. Noir is charging $50 for a table for two; it was charging $62 for seating at a communal table with chairs provided, but that arrangement is sold out. A Dîner en Blanc slot was $68.50 for two.
There is another difference. Dîner en Blanc, which began more than 25 years ago in Paris, is a commercial enterprise run in its various cities by volunteers.
Dîner en Noir, also staffed by volunteers, plans to donate all proceeds that exceed expenses to Philabundance, the Philadelphia hunger-relief group. Both Blanc and Noir have to pay for services, including legal and administrative work.
DiBona said: "I'm happy that they are celebrating the city, but I'm hurt by the assertion that this is for people we left out. It was a software glitch."
On social media, Dîner en Blanc's critics call it "elitism," DiBona said. "That's unfair."
Next year, she said, Dîner en Blanc will have a "whole new system."