Justin Timberlake fans upset after star postpones concert at the last minute

The first of Justin Timberlake's two concerts at Madison Square Garden was postponed late Wednesday due to an unspecified health issue that plagued the pop star.

Timberlake tweeted at about 5:30 p.m. that the 8 p.m. show was not going to take place as planned.

Timberlake also apologized on Twitter and added, "It kills me to have to do this. I hope to see you all on Friday."

On its website, MSG says ticketholders can get a refund if they want, starting Thursday morning.

For 24-year-old Haydee Lopez, news of the show's postponement came too late. She and her boyfriend arrived at Madison Square Garden at 7:15 p.m., only to be turned away by a security guard.

"We were literally stopped by a security guard at the door," she told FOX411. "We were handed like a sheet of paper to explain what would happen and why. It was definitely really disappointing to find out it was canceled and at the last minute."

She said her boyfriend, who purchased the tickets, had missed a 7 p.m. phone call from Madison Square Garden's customer service line, attempting to inform them about the postponement shortly before the show was set to start.

But for the Timberlake fans Lopez encountered outside the venue, who had traveled from New Jersey and Pennsylvania to see the show, an hour's notice just wasn't enough.

"I hope they’re somehow reimbursed in a way for their travel costs," she said.

And judging by the Twitterverse's reaction to the date change, Lopez was not the only one unhappy with the way the concert change was handled.

"my sister flew all the way to new york just to see justin timberlake at madison square garden & he cancelled.." one user wrote, adding profanities at the tail end of the tweet.

Others complained that they had spent money to make it to the venue.

Some users added that they wouldn't be able to attend the show on Friday, and messages were posted with users attempting to sell their Friday night tickets via social media sites.

Lopez said she will be able to make it to "Suit & Tie" singer's Friday show.

Tickets for the concert originally cost anywhere from $54 to $200.

The Thursday night performance in Timberlake's "The 20/20 Experience World Tour" is expected to take place as planned.

Madison Square Garden did not respond to FOX411's request for comment.