Error loading reports integrated report server

Hello, I have a very difficult problem to solve.

I have a web application which displays reports.  All day it works fine, but sometime in the evening the reports fail to load.  On the WFE in ULS I see "Thread was being aborted" followed by "Item has already been added.  Key in dictionary: 'Exception' Key being added: 'Exception'

I can fix the issue with an IISReset (reports run after IISReset).  If I reset the web application pool it doesn't fix the issue.  HTML timeout in web.config is set at 3600, so it's not a timeout issue.

It is a SharePoint 2010 SP2 farm running on Windows Server 2008 R2.  SQL 2008 R2.  Integrated Report Servers are running SQL 2012.  Web application authenticates against ADFS server and uses custom claims to load the reports.

In the application database we are logging this error: 

Serverwasunable toprocessrequest.---> ID3242: The security token could not be authenticated or authorized.

Any ideas what is going on here?

Thanks,

Vincent

Vincent