BlackBerry Ltd (BB.TO) (BBRY.O) posted quarterly revenue that missed analysts' forecasts due to an unexpected sales decline, pushing shares down as much as 13 percent, which would be their biggest one-day drop in more than two years.The company reported that software and professional sales fell 4.7 percent to $101 million during the first quarter. Investors pay close attention to that category because growth of high-margin software sales is at the heart of Chief Executive Officer John Chen's turnaround strategy for the company. Its stock had gained about 60 percent over the past quarter on expectations that sales of new software products are starting to take off.