- Event not fired.
- Microsoft.Reporting.WebForms.HttpHandlerInputException: Missing URL parameter: IterationId
(This is only part of the long error message).
- Report loads forever (never stops loading).
On the aspx page, add attribute: EnableEventValidation="false"
For my particular case, I was trying to display a report (SSRS), and it never stopped loading. However, for my case, it was because of the version of the Internet Explorer (yes, the report is only compatible with IE for mine). After changing the version of the IE through developer tool (F12), I managed to display the report properly. You can also try to display the report from another machine using the intended IE version to see if it displays properly.