A software firm brought in to make two Somerset councils and the police more efficient has made duplicate payments to suppliers totalling £4.6m.
SouthWest One used a software program called SAP to pay the suppliers to Avon and Somerset Police, the county council and Taunton Deane Borough Council.
Delays in the automated system resulted in SouthWest One staff sending out cheques to prevent further delays.
The firm's spokesman said more than 95% of the money owed had been recovered.
Since SAP was brought in two years ago about 2,200 bills were paid twice, and £200,000 remains outstanding.
John Wilkins, the chair of the Audit Committee at the county council, said: "Somerset County Council has always had an excellent reputation with making payments, and their finance department and our reputation suffered quite significantly because of the problems of the introduction of this particular system."
Mr Wilkins said it happened because the computer system delayed payments.
To counteract this, finance staff would send out a cheque so suppliers did not have to wait, but afterwards the automatic payment would also be made.
This resulted in suppliers receiving a double payment, the biggest of which was an overpayment of £800,000 to First Group from the county council, which runs some bus services in Somerset. The bus firm has repaid this sum.
The county council paid out £3.6m and is still owed £169,000 but has plans in place to recover £110,000 through instalment payments and take legal action where necessary.
It also said the amount still owed was a "tiny" proportion of its overall budget and no service had been affected as a result of the mistake.
The police paid out £404,000 and is still owed £10,426.
Avon and Somerset Police said the "vast majority" of its money had been recovered and it had plans in place to recover the outstanding sums.
Taunton Deane Borough Council paid out £517,000 and still has to recover £12,200.
Leader of the Conservative-led borough council, John Williams, said: "We did have teething problems which I regret, which SouthWest One regrets, but now we have worked through that and we have become more efficient."
A spokesman from SouthWest One said: "SouthWest One has worked jointly with Somerset County Council to recover more than 95 per cent of all duplicate payments.
"We continue to work together to recover the outstanding amounts and improve processes to minimise the risk of further repeats."