Michael Jackson said these shows will be his last in the UK
Singer Michael Jackson has added more dates to his residency at London's O2 arena in the summer.
The veteran pop star recently revealed 10 dates, but after pre-sale tickets sold out on Tuesday, 14 more dates have been announced on his website.
However, some fans who had registered experienced problems trying to buy tickets due to "technical problems".
Ticketmaster's managing director Chris Edmonds said there had been "an unprecedented level of demand".
"Unfortunately due to a technical issue, we were unable to facilitate all immediate ticket requests.
"Apologies to those fans who were unable to log on, but fans should keep on trying to purchase tickets."
Additional codes were being issued as new shows were added, the organisers said. Registration was being dealt with on a first come, first served basis.
The pre-ticket sale will close on Thursday, or until they have all been sold.
The rest of the tickets will go on sale to the general public from 0700 GMT on Friday.
Tickets for the Jackson shows are already being sold on the online auction website eBay.
Prices on the site range from £170 to £10,000, but tickets bought directly from the singer's website or Ticketmaster cost up to £75.
Jackson, who has won 13 Grammy awards, has said this will be the last time he will perform in the UK.