ReportViewer control with a Web Farm

[Guest]

I'm having issues with the reportviewer control. When viewing the regular
report it works just fine. However, when an export to PDF or Excel is
attempted and the load balancer sends the export request to another server I
get the following error:

ASP.NET session has expired

It looks like the download goes to a page
"Reserved.ReportViewerWebControl.axd" and tries to grab the report it just
built but can't find it to download it. We have the machine keys the same on
all the servers in the web farm. Is there anything else I should try?

Regards,
David Gardner