AUTHOR: Marin Bratanov
DATE POSTED: June 04, 2018
When executing this page directly from the application server everything works as expected.
Basically, the Telerik controls do not work behind a reverse proxy (ARR).
The problem is most likely due to the fact that the proxy server is caching the HTTP handlers we use to get the needed WebResources and this makes them invalid. For this reason the controls are unable to load their scripts and resources and do not work.
The Telerik UI for ASP.NET AJAX controls rely heavily on WebResource requests to fetch the necessary scripts and styles they require to operate. This is the standard (default) way to fetch resources in the MS AJAX library and if it does not work, it is likely the the framework itself will not operate. Thus, Telerik UI for ASP.NET AJAX does not officially support (reverse) proxy scenarios.
You need to ensure that all requests return successfully.
To fix it you can try the following: