Up to 1,500 junior doctors offered posts as registrars have had their job offers withdrawn, following a mistake in the recruitment process.
Doctors say they have been left stressed and in limbo, and potentially out of pocket over plans to move home.
The Royal College of Physicians, which oversees recruitment, apologised for the "human error" and is working over the weekend to restart the process.
Doctors' union, the British Medical Association, said it was "appalled".
The junior doctors were alerted to the error just before 17:00 BST on Friday, at the start of the bank holiday weekend. Fellow doctors described juniors as being in tears.
Many were set to uproot their families to take up the job offers, selling homes, putting offers down on houses, moving children to new schools and partners resigning from jobs to find new ones.
A nationally co-ordinated system, known as ST3 Recruitment, is used for recruiting doctors across England, Scotland and Wales into a broad range of specialities.
Last month, after attending interviews, up to 1,500 junior doctors entering their third year of specialist training received job offers in 24 different medical fields.
Each candidate was given a score which determined how likely they were to get their choice of hospital and specialty.
On Thursday, the Royal College of Physicians (RCP) discovered a significant number of candidates were credited with the wrong score, because of an error transferring data from one computer programme to another - and may therefore have received an incorrect job offer.
On Friday, the RCP wrote to all those who had offers to say it was being rescinded.
"We are deeply sorry that it has been necessary to rerun the ST3 offer process due to a mistake in this round of processing," the letter from the RCP said.
"We have taken this approach to be fair to all candidates which can only be achieved with the real scores used."
In an updated statement,, external the RCP said it was working through the weekend to restart the recruitment process but it will take more than a week until the first offers start on Monday 14 May.
It acknowledged the "bad timing" of the announcement but said "we decided that it would be even worse to keep the information to ourselves for three days" and wanted to be "as transparent as early as possible".
Speaking on behalf of the junior doctors, the BMA issued a statement saying: "We cannot express how unacceptable we find this situation."
It said it had caused extreme anxiety for trainees and lamented "the impact - both emotionally and financially - it is having on junior doctors across the UK".
Chairs Chaand Nagpaul and Jeeves Wijesuriya said they had spoken at length with Professor Jane Dacre, president of the Royal College of Physicians, "to articulate the strength of feeling".
"We have heard from trainees who have, after receiving these job offers, put down deposits on homes, arranged moves or whose families had adjusted their plans," they said.
"We have conveyed our expectation that college will support and compensate these trainees for any inconvenience."
The BMA said it would take legal advice regarding a possible breach of contract, and compensation.
James Savage, 28, ended talks with other potential employers when he received his first choice job offer in renal medicine in the West Midlands.
"It's not well understood how much we move around as junior doctors.
"You move jobs every four months, hospitals and even locations every year. So these contracts were an offer of stability for the first time.
"Our morale is already extremely low. This isn't going to help things."
Liver doctor Ben Hudson said juniors were "in tears" while the RCP was "carelessly playing with people's futures".