Dozens of reports from WebmasterWorld claim that Google AdSense's advanced reports are having major downtime issues. The errors people have been seeing are:
Report generation failed
There was an error in generating the report you requested. Please try again later.
First reports came in at about 8:45pm (EST) and the issues still appear to be bogging down some AdSense publishers. I tried a few reports and they worked for me, but maybe my advanced reports are not advanced enough?
Reportedly, it has been mostly down for the past 12 hours but there are times that the advanced reports work. Seems server resources related to me.
Forum discussion at WebmasterWorld.
Update: AdSenseAdvisor early Thursday morning (March 27th) responded saying it has now been resolved:
Thanks for all of the reports. I have just heard back from our engineers, and they have now resolved the issue. Please let me know if you are still having trouble with your Advanced Reports page.