The reports are generated on the server and are served through the http handler to the ASP.NET ReportViewer
. This means the whole report instance with its resources is kept in session, so that it is available for the report viewer to page, print and export. If the session expires the resources will be lost and there may appear similar issues. For more details take a look at the Report is unavailable or session has expired error message
KB article. Thus check the session state
timeout and try to extend it.
To improve the performance and control where resources are cached you can configure the application to use File or Database reporting cache
provider. Using File cache provider, you will need to grant the users access to the set folder.
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