Research in Motion has admitted that the outage which bought down its entire North American and Canadian network was caused by a system upgrade that went wrong.

RIM's network crashed for several hours last week for the second time in a year, turning off all Blackberry sets. A RIM spokesman said an internal data routing system within the BlackBerry service infrastructure that had been recently upgraded crashed.

RIM has being trying to upgrade its capacity lately and has been making similar upgrades throughout its network without any problems. No messages were lost during the outage, which once fixed, sent them on as normal.

However the outage outraged many businesses who depended on the smart phone to keep in touch with their staff. After the last outage last year there were questions about how reliable RIM's network was.