BlackBerry maker Research in Motion is blaming last week's wireless email outage on a bad update to its caching system.  

The company said in a statement that the update was not expected to have any impact on the BlackBerry infrastructure, but admitted that it had done insufficient testing.

The flawed update prevented all communications between the system's database and cache. The company then attempted to move to a back-up server, but this process failed causing a further delay in restoring the service to users.

The BlackBerry service was out for roughly 12 hours between Tuesday evening on 17 April and Wednesday morning on 18 April. The outage only affected accounts in the US, including users who were roaming in other regions.

The wireless email service for North America relies on a single data centre in Canada.

RIM apologised for the outage and said that it had revamped its testing and recovery procedures to prevent similar issues in the future.