“How can anyone invest tens of millions of dollars, over a period of months, by mistake? And how can that person fail to notice that he owns three-quarters of the stock in one public company, and a third of the stock in another?” asks Floyd Norris in today’s New York Times.

“Those are the questions that investors have for Scott R. Sacane, a Connecticut money manager who has disclosed such purchases in recent days. The purchases left funds he manages owning a 33 percent stake of Esperion Therapeutics and 78.5 percent of Aksys Ltd.”

M”r. Sacane conceded in his filings that he should have disclosed his holdings much earlier. In April, he had promised to stop buying Aksys shares.”

“For investors, the bad news is that large portions of the shares in each company are held by an investor who said he did not intend to buy them, creating a potential overhang of shares whose sale could devastate the share prices. They have fallen sharply since news of his holdings came out in recent days.”

“In filings with the Securities and Exchange Commission, Mr. Sacane, who runs Duras Capital Management of Norwalk, Conn., said he had acquired the shares inadvertently.”

“The filings did not offer much in the way of additional information on how the errors occurred. But they made clear that they had happened over an extended period.”

” ‘It’s unbelievable,’ said William C. Dow, the chief executive of Aksys, adding that Mr. Sacane told him that three layers of software had somehow failed, leaving him ignorant of the purchases.”

” ‘He just wanted to assure us there was a breakdown of his internal controls,’ Mr. Dow said, adding that he found it hard to believe that no one at Duras had noticed what was happening.”

“Mr. Sacane told Aksys, a maker of a machine for home kidney treatment, of his continued purchases on Thursday after the stock market closed. He told Esperion, which is developing products for the treatment of cardiovascular disease, of a similar error on Friday, according to his S.E.C. filings.”

“In both cases, Mr. Sacane’s purchases blew through limits established by poison pills that the companies had issued. The pills, known formally as shareholder rights plans, threaten dire consequences to shareholders who acquire too many shares without the consent of the board. Esperion has twice cut deals with Mr. Sacane to keep the pill from taking effect, the first last November and the second one yesterday, according to Mr. Sacane’s filings.”