NHS Connecting for Health has postponed the release of updated choose and book software after the current version gave some patients other people's appointments.
Version 4.0 of the software will enable appointments to be booked at any centre in the country that is able to provide a patient's care. It was due to go live on 12 April. However, it was postponed after a glitch with the current 3.6 release emerged on 11 April.
A spokesman for CfH, the agency responsible for implementing the national IT programme, said: "The system mixed up patients basically and gave them someone else's appointment place and time.
"We have postponed the changeover to 4.0 until we have fully identified what the issue was."
He added that the problem had affected "only a couple of hundred" patients and that CfH hoped to resolve the issue "in a matter of days".
Version 3.6 enables appointments to be booked at any local centre. The spokesman said that if a patient wanted to be treated further afield, their GP could arrange this by bypassing the choose and book system and sending a referral letter.