WATERLOO, Ontario ? If you own a BlackBerry, you already know this story. Research in Motion, which makes the BlackBerry, experienced a significant outage of its wireless email service on Monday, its second nationwide disruption in the last 12 months.

The company notified its customers of the problem Monday afternoon, saying that the outage was affecting about 50 percent of North America.

RIM didn’t return calls seeking comment, The Wall Street Journal reported.

In its notice to customers, RIM said the cause of the outage was “to be determined.” It follows a similar outage last April, which was caused by an improperly tested software update at the company’s data center that handles BlackBerry email traffic for millions of users.

At the time RIM, warned that its backup systems didn’t perform as planned, raising further concerns among customers and investors about whether RIM’s infrastructure can keep up with its torrid growth. RIM added 1.65 million subscribers in its quarter ending Dec. 1, 2007, bring its total to 12 million world-wide.

RIM, whose email service is widely relied on by corporations and governments, is uniquely vulnerable to such large-scale outages. All emails sent through its enterprise servers are routed through a network operating center, which has several locations. A breakdown at the network operating center can therefore quickly disrupt service nationwide.

RIM’s stock fell $1.32, or 1.4 percent percent, to $93.15 in after-hours trading.

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