Houghton Mifflin Harcourt CEO Barry O’Callaghan has resigned. According to a spokesperson, he will remain as a senior adviser at the company.  CFO Michael Muldowney has been asked by the publisher’s board to serve as interim CEO.

O’Callaghan’s Riverdeep Houghton Mifflin Group bought Harcourt in 2007. Last year, the CEO commented on the company’s struggles to refinance its debt: “Nobody has lost more on paper than I have. Obviously I’m disappointed for my fellow shareholders, but I can’t be blamed for things I can’t control, and unfortunately state budgets are things I can’t control.”

Former CEO Tony Lucki retired in 2009.  O’Callaghan–the CEO of Education Media & Publishing Group, the Dublin-based owners of the conglomerate publisher–replaced him.