Boston Scientific Corp. said it found accounting irregularities at its Japanese subsidiary that resulted in $40 million to $50 million in improperly recorded sales in the first nine months of 1998. The Natick, Mass.-based company, one of the top three U.S. makers of stents that prop open blood vessels, said it is investigating how far back the problem goes. Boston Scientific said it has replaced the heads of its international division and Japanese unit as it continues its probe of the irregularities. The problem indicates that the company's Japanese operations aren't as strong as previously thought and comes a few weeks after the company recalled a product and then delayed reporting its third-quarter earnings. Analysts said they're now not sure how to forecast the company's performance. In a conference call with analysts and investors, Chief Financial Officer Lawrence Best vowed to correct the problem before issuing third-quarter results and said he hoped it wouldn't have any impact on fourth-quarter earnings. Trading in Boston Scientific shares was halted on the NYSE pending the announcement. Before the halt, the share price fell as much as $7.25 to $45. The stock last traded at $46.38.