Thanks for your response. The error message you shared in the screenshot is generated by AWSSDK.Core library and the front end application displays this error message in a popup (as shown here). The viewer control in the showcase application consists of two layers. When the document is displayed inside the viewer control, the first layer (showing “Loading your content…”) gets hidden. Whereas, in case of any error, the content of the document is not displayed in the viewer control and therefore, you are able to see the first layer saying “Loading your content”. This behavior is not related to any feature of the GroupDocs.Viewer for .NET API and is specific to the front end application.
Please note that the applications provided in the Showcase are to demonstrate the implementation and working of the features exposed by GroupDocs.Viewer API. As these applications are open source, you can feel free to modify them as per your requirements. We would also recommend you try out our more improved and enhanced open source applications listed below.