The stock is down 7.3% at midday following the book chain’s warning last night that there’s bad news ahead regarding its NOOK e-readers and tablets. It now forecasts that NOOK revenues for the fiscal year that ends in April will come in below $3B, with a cash-flow (EBITDA) loss that will be “greater than it was in fiscal 2012.” That contradicts Barnes & Noble‘s assurance last month that the NOOK unit would generate revenues of about $3B, with a cash flow loss “at a comparable level to fiscal year 2012.” And it makes 2013 the third straight year that Barnes & Noble will miss its guidance, Maxim Group analyst John Tinker notes. The NOOK business “is proving to be expensive — and with slowing revenues makes spinning it off to tech investors harder,” he says. “At some point the company has to quantify the amount it is prepared to lose.” The company says it will report earnings for the three months ending in January on February 28, later than it tentatively planned. B&N owns about 78.2% of the NOOK Media subsidiary, while Microsoft controls 16.8% and Pearson has 5%.