"Although the system is designed to failover to a back-up switch, the failover did not function as previously tested. As a result, a large backlog of data was generated and we are now working to clear that backlog and restore normal service as quickly as possible," RIM said in a statement.

The new crisis comes as RIM is fighting off agitated investors that are asking the company to explore strategic options and a new leadership. The Canadian company is also fending away competition from Apple's iPhone and phones running the Android operating system.

"You've depended on us for reliable, real-time communications, and right now we're letting you down," Bienfait said in the letter. "We are taking this very seriously and have people around the world working around the clock to address this situation."

In a conference call earlier on Wednesday, David Yach, RIM's chief technology officer for software said that there was no evidence of a breach or a hack. He did not provide information on how many customers were affected, saying that different customers were affected differently, with some not at all affected.

The backlog and queuing of messages starting in Europe caused some impact in nodes in other geographies, Yach said.