Airline caterer Alpha Airports has said legal uncertainty surrounding one of its contracts was behind the decision last month to pull its shares from the London Stock Exchange.
Although the group would not go into detail, it said there was doubt over whether a major contract, which began in October 2005, was a genuine transaction.
Trading in its shares was suspended when accountant PricewaterhouseCoopers refused to sign off its accounts for 2005 due to the irregularity.
In a statement to the City, Alpha said: "Material aspects of these new arrangements may not have been intended to have proper commercial effect."
It added that the client "might have been able to manipulate its own financial statements in circumstances in which its parent company was preparing for an initial public offering".
Two non-executive Alpha directors have been appointed to investigate the matter.
Total revenue from the deal in question was about £7.5m, which the group said it has received in full.
By Tom Bill