There are reports in the Microsoft Advertising Forum that advertisers can't login and when they can, the reporting is delayed.
Here is the error advertisers were getting:
Microsoft adCenter is experiencing problems Microsoft adCenter is experiencing a problem that prevents it from continuing. Information that can help resolve the problem is now being sent to the adCenter site maintenance team. You can return to the Microsoft adCenter sign-in page now, or sign in again later. We apologize for the inconvenience, and thank you for your patience. Return to the Microsoft adCenter sign-in page.
Microsoft blogged about the issue and then late last night updated the post to say it was resolved. But it will take time to catch up.
Tina from Microsoft said:
The adCenter UI issue has been resolved as of 11:45 PM PDT today; your account and campaign details are now accessible. Issues with the API are still being addressed and report data may be delayed up to 24 hours. We will update this post with additional information as it becomes available.
So keep this in mind when checking your reports today.
Forum discussion at Microsoft Advertising Forum.