Hello James,

I am sorry to hear that you had trouble finding information about that error.

I was able to find the article in the Telerik Reporting document by searching some of the keywords of the error such as "CacheStorage", "Error registering the viewer", etc. but indeed, nothing meaningful would show up when searched in the Telerik Report Server documentation.

I would advise, in the future, to always check both documentations as the Telerik Report Server product is built on top of Telerik Reporting. On our side, we will try to include the information, from the linked articles in my previous reply, in the documentation of the Report Server.

Please accept our apologies for the caused inconvenience.

Regards,
Dimitar
Progress Telerik

Hello James,

Thank you for the screenshot!

The error indicates that the first request made by the viewer to the REST Service that attempts to utilize the Storage fails. This is the request for registering the viewer/client.

Usually, the error occurs because the storage is in a corrupt state. The NullReferenceException is thrown because the engine tries to read a non-existing resource from the storage. Such issues are rare but happen mostly with the FileStorage instance, because it is more susceptible to external factors that prevent the correct writing in the storage asset files (i.e. write delays, antivirus programs that could lock the file while inspecting it, etc.).

The easiest to resolve this issue, usually, is to delete the folder with the cached assets. For Telerik Report Server, if FileStorage is used, that would usually be a folder with a randomly generated name(GUID) at the following path:

C:\Program Files (x86)\Progress\Telerik Report Server\Telerik.ReportServer.Web\Data

Delete the folder with the randomly generated named, for example, 8963c32d, and restart the application. Do not delete the TRS folder because that is the folder with the actual Report Server assets such as the TRDP/TRDX files, for example.

If that does not help, please check the Telerik.Reporting.Cache.CacheStorage.AddInSet NullReferenceException KB article for more possible ways to tackle the problem depending on the particular environment.

If further assistance would be needed, you may follow the Troubleshoot Report Server Manager - Telerik Report Server KB article to send us more information about the scenario in a separate ticket.

With that being said, the status of the item will be changed to 'Declined'.

Regards,
Dimitar
Progress Telerik