DENVER (CBS4) – Some Denver International Airport travelers are grumbling because when they missed their flight because the trains at the airport broke down on Friday they were charged “change fees.”

4 On Your Side Money Saver Suzanne McCarroll looked into whether the fees were charged in error.

Technically it wasn’t an airline problem, but it became a major hassle for the airlines as hundreds of passengers missed their flights. The automatic trains stopped working at 7:30 a.m. A software problem was to blame.

For the next two hours airport crews were able to operate the trains manually, but there were fewer trains running and they were slower. That led to horrendously long lines at airport security.

All passengers were funneled to Concourse A and then bussed to their gates on the B and C concourses.

“We arrived, we were almost two hours ahead of our scheduled departure time and we had to wait in line a very long time,” a passenger said.

It was long enough that they missed their flight and the family spent hours on the airport floor.

Some passengers were charged change fees by the airlines Friday for missing their flight.

“When I talked to a customer service manager, her reply to charging me a change fee was … it wasn’t her fault the train was down,” traveler Lana Covey said in an email to CBS4. “This is how they treat residents of Colorado? Has anyone else had problems with Frontier Airlines charging a change fee?”

McCarroll contacted a Frontier Airlines spokesperson who says she should not have been charged a change fee and that it was an error. United and Southwest airlines also waived change fees on Friday, but for those passengers who were erroneously charged the airlines say to contact them for a refund of that fee.

In the early morning hours some of the ticket agents were not yet instructed to waive the change fee.