A weak earnings report this morning put an untidy bow on what has been a sloppy year for Barnes & Noble (NYSE: BKS). The bookstore chain reported a loss of $57.7 million, or $1.08 per share, for its fiscal fourth quarter, which ended on April 28. That’s slightly less than the $59.4 million loss the company suffered a year ago, but more than the 92 cents-per-share losses analysts were expecting. The poor earnings have sent BKS shares tumbling 5% in mid-day trading. Over the past 12 months, Barnes & Noble’s stock has now fallen 25%. Book sales nationwide have been slumping, eroding earnings for the largest traditional book retailer in the U.S. Barnes & Noble has tried to branch into the lucrative mobile device business, introducing a Nook Tablet e-reader in November and convincing Microsoft (Nasdaq: MSFT) to invest $300 million in it. Today’s earnings announcement revealed, however, that Nook sales are slowing. Revenue in Barnes & Noble’s Nook unit declined 11% last quarter, though sales were up 34% for the fiscal year. Competition is about to get even stiffer in the electronic tablet business, however. Microsoft announced today that it’s coming out with its own e-tablet, called the Surface. Et tu, Microsoft? So yes – on top of the fierce competition Barnes & Noble already has to contend with from Apple’s (Nasdaq: AAPL) iPad and Amazon’s (Nasdaq: AMZN) Kindle Fire, BKS now has to contend with a new product from the very company that just invested in the Nook. That’s bad news considering Nook sales already trails those other e-tablets by a considerable margin. With the e-tablet market expanding, Barnes & Noble may to find new revenue streams if it hopes to become profitable again.