Hey, so we have been running DNN for 5-6 years. We also host a DNN site for one customer. On our site that we don't really update anymore, we are running DNN 7. For our customer, we updated to DNN 9 last summer. 
The issue: Previously we have been able to add images or documents using the "Insert Media" button in the text editor. 
When we try to do that now, instead we get this error message: "Web.config registration missing! Telerik dialog require a HttpHandler registration in the web.config file. Please, use the control's Smart Tag to add the handler automatically, or see the help for more information: Controls > RadEditor > Dialogs > Introduction".
So this is a issue for both sites, and that our site isn't updated to newest DNN seems irrelevant. 
Last time adding images worked, was in late november/start of december. After that, noone attempted to add anything until mid january. 

I had never heard about Telerik before I saw this errormessage. How I understand it is that it's built into DNN/DNN uses it's library for texteditor etc? 
I have tried following steps from this page: https://www.telerik.com/s...the-web-config-file-
Without much luck. Struggling to see how I can even start the "control's Smart Tag", from the images over on the telerik documentation it seems more like something I would see if I were a developer using DevExpress, not for a end user in DNN.

Any advice/tips would be really appriciated.
Regards.