Ssrs reports error when large number of parameters are passed

Now where you can find this web.config file?

If using SharePoint integration Mode: It’s located on the web server and has the path C:\inetpub\wwwroot\wss\VirtualDirectories\80\web.config

But you have to keep on mind if there is more than one SharePoint instance and what instance are you using to deploy the reports, of example the path can be C:\inetpub\wwwroot\wss\VirtualDirectories\EPMA\web.config

If using SSRS native Mode: The web.config file will be located at your SQL server and it will have the path: C:\Program Files\Microsoft SQL Server\MSSQL\Reporting Services\ReportServer.

The solution for this issue is to add a section in your web.config file inside the <appsettings/> section

<appSettings>

    ...

    <add key="aspnet:MaxHttpCollectionKeys" value="9999" />

    ...

</appSettings>

That 9999 value should represent the number of parameters that you believe it will be used.