The NHS IT upgrade is a multi-million pound project
Patients with suspected cancer have had urgent appointments postponed at a top London hospital because of problems with the new NHS computer system.
It is one of a series of problems faced by Barts and The London NHS Trust since the IT system went live in April, according to Computer Weekly magazine.
Other issues include patients being booked into closed clinics and repeatedly cancelled appointments.
A spokesperson for the Trust said there had been no clinical harm to patients.
A total of 11 patients with cancer have had urgent appointments postponed for between two days and a month - the government target states that every patient with suspected cancer should be seen within two weeks.
The delay was "directly attributable" to problems with switching outpatient information to the new system, a report presented to the Trust board said.
The upgrade of the NHS IT programme is set to link more than 30,000 GPs in England to nearly 300 hospitals by 2014, and includes an electronic medical records system and e-prescriptions.
The Care Records Service at the hospital is the biggest system installed in the NHS so far.
Members of the board also heard that the hospital is not receiving any money for treating patients because the records of what work has been done are not reliable.
There are also problems with meeting the four-hour wait target for seeing emergency patients because staff are struggling with the new system.
The Millennium software system used at the Trust was provided by Cerner for British Telecom who are charged with upgrading IT in the London region.
Tony Collins, executive editor of Computer Weekly magazine said there had been a lot of secrecy and defensiveness around the NHS IT programme but it was important for other Trusts to learn from the problems.
"It would be wrong to say this was the fault of the computer system as it works in the States the problem is with getting people to adjust to a different way of working along with some technical issues.
"Other trusts will need to learn from this."
Richard Bacon MP, a member of the Public Accounts Committee which last week held hearings on the latest National Audit Office report on the NHS IT programme said: "The latest revelations from Barts show that this is not just a story about IT.
"These failures directly threaten the standard of care offered to patients ¿ in this case, patients with suspected cancer. It is hard to imagine a more serious failure." A spokesperson for Barts and the London said those patients waiting 31 days had been offered sooner appointments but chose to stick to the original date.
Professor John Toy, lead cancer clinician at Barts and The London NHS Trust, said the aim of the two week wait for suspected cancer was to impart a sense of urgency but not necessarily emergency.
"I am confident that none of these patients will have suffered clinical harm."
Charles Gutteridge, medical director at Barts and The London NHS Trust said they had expected there would be major challenges to implementing such a large system.
"We apologise unreservedly to the patients, GPs and staff affected by these difficulties, and are working urgently to resolve them through an intensive programme of measures."