Getting this error in the browser when trying to preview a report:

Error registering the viewer with the service.
An error has occurred.
Incorrect value (null) deserialized. Make sure you are using CacheStorage inside single-instance application deployment only.

A possible reason is the cache for the Report Server used for previewing reports has become corrupted. A workaround is explained in the Telerik.Reporting.Cache.CacheStorage.AddInSet NullReferenceException KB article.

It will be very convenient for the user to be able to clear the cache directly from the Report Server Manager UI.

The Whitelabeling option are extremely limited.

I would like to see more customization available like removing the sidebar completely, or based on user settings / roles - as well as the top title bar (where logo is).

Customizable themes would go a long way.

Being able to integrate the existing report server pages into our own website would cut down on a lot of work.

Functionality for capturing user activity like executing reports from viewers or through the Report Server Web API.

Provide the option to save custom report settings in the storage and enable specific rendering device settings based on custom settings.

Example use case:

- on the Report Server - Report view, the user should have a button for report settings;

- this button will open a custom dialog that contains various inputs;

- clicking Save on the custom dialog, the save operation will be handled by the Report Server implementor and the implementor should be able to get the user input and save various settings in the Report Server storage for the selected report;

- on rendering the report through the Preview, Scheduled Task, or Data Alert, the report server engine should invoke a custom event/code that can read the storage report settings and based on them provide rendering device settings to use during the report rendering.

If you set a default value of integer subreport parameter to '3233' or another valid integer, when executing the main report there will be an exception stating that the value for this parameter is not valid and the report processing is canceled. The parameter exists only in the subreport and not in the main report.

The error disappears if the value of the parameter is set with an Expression, for example, '=3233'.

User functions should be visible in Edit Expression editor when editing Report Server's report in Standalone designer.

Considering that the server's configuration was modified to load the custom assembly with user functions as per How to configure Telerik Report Server to use reports with custom functions, there should be no other configurations required.

As a user utilizing the Report Server product, I need to use a single instance of it to serve two or more completely separated divisions/clients so that they do not have access to each other's assets, so that I do not have to make two different deployments of the server and support them. See https://en.wikipedia.org/wiki/Multitenancy

Reports with resources for different languages should be rendered with the language resources and client culture.

• Preview - render the reports according to the browser settings/language;
• Scheduled Reports and Data Alerts - language/culture option is needed for every recipient;
• Server API - have to accept device info or language/culture option;

We have standardized the usage of Central Identity System across applications using OAuth and OpenId connect based https://identityserver.io/.

As a report editor, I want to authenticate to report server frontend using IdentityServer.io Single sign on. 

As IdentityServer is .net server core based, we would like ReportServer also .net core based to support non-windows hosting scenario.

In order to provide better data-driven subscriptions implementation, the subscribers of a Scheduled Task or Data Alert should be modified dynamically. Currently they are a static list of emails, which is not convenient when a report must be sent to a whole group of users in an organization, because the group members can constantly fluctuate.
Report Server should provide the option to declare an external data retrieval service in the ST/DA subscribers list. This service could be a REST API endpoint or a file path that will return the list with the subscriber emails.

After changing the culture settings on the server machine to EN-GB (which should display the date in dd/MM/yyyy format), the Preview of the report parameters still shows the date format as default, in US format (MM/dd/yyyy).

However, I would not expect to have modified the code to fix this, it should be a configurable option and/or take local server formatting.