Error Promise is undefined
|Product||Progress® Telerik® Report Server|
As of Telerik Reporting R2 2017, the Report Server and HTML5 Report Viewer require a browser supporting promises.
The error indicates that the used browser does not support promises. Please follow the HTML5 Viewer: Important Settings article which contains the requirements for promises.
Add a promise polyfill to the page, such as Polyfill.io.