For about two hours, Microsoft’s Office 365 and other cloud-based services were inaccessible by thousands of people in Chicago, Denver, New York City and other North American areas yesterday.

Those who migrated to the relatively new platform were unable to check email or use Outlook, and system admins were unable to add, remove or change any user accounts. Some reported not being able access or share documents on SkyDrive. And during this crisis, users couldn’t report the problem since even Microsoft’s Service Health Dashboard was down for part of the time.

Two hours feels like forever in these situations, as shown by Microsoft’s relevant Twitter streams and software forums filling with angry criticism and doubts about the wisdom of relying on cloud services. The company began responding within about 20 minutes, reassuring users that it was aware of the problem and working to fix it as quickly as possible.

Microsoft’s Steven Gerri, General Manager, Global Foundation Services, issued a statement explaining what happened. “At approximately 11:30am PDT, Microsoft became aware of a networking issue affecting customers of some Microsoft services hosted out of one of our North American data centers,” it read. “We worked to isolate the issue and we are beginning to see service restoration. We continue to investigate the root cause of this issue.”

Microsoft launched Office 365 in June, promising a 99.9 percent level of uptime.

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Photo by flickr user BasicGov, used under Creative Commons license