I am also getting this issue after migrating from Kentico 7.0 to Kentico 8.0. All of the reports in the Web Analytics section of the site are broken. Here is one example error:
11/26/2014 9:42:56 AM
Message: Report graph 'pageviews.weekreport.graph' not found.
Exception type: System.Exception
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
This is happening for all of the analytics reports.