Emerson Hospital of Concord, MA is conducting an investigation into an accounting error that caused it to overstate its 2006 financial results. The disclosure comes as the hospital's finances appear to be deteriorating. It posted solid profit margins and surpluses in fiscal years 2004, 2005, and 2006. But in the nine months that ended last July, the hospital lost money providing healthcare and avoided losses only because of other income, such as profits on its investments.