Westlife made an on-stage apology after hundreds of furious fans were told to 'stand or go home'.
Elderly and disabled concert-goers, who were physically unable to stand for the sell-out show, were forced to leave - despite some paying £200 for a ticket.
Disgruntled crowds were told less than an hour before the boyband were due on stage at the SSE Hydro last night that their seated tickets were no longer valid.
Some fans splashed out more than £1,000 for VIP experiences to catch the band's 'Twenty Tour', with most stumping up for tickets months in advance.
Traffic delays led to the failure of vital equipment - needed to make a stage level seating area - not turning up at the venue, organisers claimed.
The SSE Hydro posted a statement on its Facebook page minutes before doors opened to the concert telling fans they would have to stand or request a refund.
One group of devoted fans had to travel back to Aberdeen the same night, while others said they were offered alternative seats 'nowhere near' their original ones.
Furious fan Sophie Campbell does not go to gigs often due because of her asthma but made an exception to see Westlife with her disabled mother Margo.
Sophie paid for front row tickets, but when she arrived was told to stand and claims staff refused to give her disabled mother a wheelchair to sit in.
Sophie said: "I don't go to concerts to stand because my asthma is too bad, small enclosed spaces don't work for me.
"I was told when I got here I could stand or get a full refund. That's all.
"I asked for a wheelchair for my disabled mother and was told she can either deal with it and stand or go home and come back to the Hydro tomorrow for a refund, so I've got to drive all way back to Glasgow for a refund."
Niki Kane was having her tickets scanned at the door when she was told she and her group of six friends would have to stand.
She explained to staff that three of the group suffered from arthritis, sciatica and fibromyalgia, and so could not be on their feet for a prolonged period of time.
Niki said: "We were told to either stand or leave and try for a refund but it would not be guaranteed.
"There didn't seem to be any organisation or concern for the interest for ticket holders."
The band apologised to crowds on behalf of themselves and their crew and said transporting production equipment from Belfast was the cause of delays.
Singer Nicky Byrne said: "The options were, at 7 o'clock tonight, no show or give them the best show that we could give them, which would mean standing on the floor for you guys.
"Rather than send you all home and postpone for another night we thought we'd just go out and give them a great show.
"We hope you don't mind.
"So thank you for being so understanding. We really appreciate that."
A spokesperson for the SSE Hydro said: "The seating layout for tonight's Westlife show was changed due to unexpected transport delays.
"For ticketholders who did not wish to or were unable to stand, full refunds are available from the original point of purchase.
"We apologise for any inconvenience this may have caused."