The partially Chinese owned maker of the famous London taxi said it needed to restate the results of previous years because of the problems and would announce six-month earnings for the current year on or before Sept 24.
Manganese Bronze introduced a new integrated IT system in August 2010 in an effort to better manage its global supply chain. But the company said that, when it entered data from the previous system into the new one, some of the data weren't properly processed. It cited "a combination of system and procedural errors," as the reason for the mishap.
"This problem led to the over-statement of stock and under-statement of liabilities in the financial statements of previous years," Manganese Bronze said. The cumulative effect of the errors was an estimated 3.9 million pound understatement of historical losses.
The company didn't say what new IT system it is using.
Manganese Bronze, which is 20 pc owned by China's Geely, is facing increased competition in the UK taxi market. In May, it said sales dropped in the first half and that it expected losses to widen during the period.
Despite its earnings slump, Manganese Bronze cited continued support from its banks and from Geely.