Good morning, Bharani!

The error may occur after changing the password for your Telerik account so that it no longer matches the one set when setting up Telerik Nuget feed - the following Troubleshooting article describes how to resolve the issue by updating the NuGet feed (Solution 1) or by using Windows Credentials Manager (Solution 2).

If the above seems as expected, I would then suggest checking if Telerik UI for ASP.NET AJAX is visible as a product in your Telerik account - https://www.telerik.com/account/downloads/product-download?product=RCAJAX. 

You can find more tips and tricks at:

• https://stackoverflow.com/questions/41185443/nuget-connection-attempt-failed-unable-to-load-the-service-index-for-source
• https://zimmergren.net/nuget-error-unable-load-service-index-for-source-unauthorized/ 

Best Regards,
Rumen
Progress Telerik

Hi Bharani,

I hope you are doing well!

The error indicates that Visual Studio is trying to download the Telerik.UI.for.AspNet.Ajax.Net45.2021.3.914.nupkg package from the following locations:

• C:\Program Files (x86)\Microsoft SDKs\NuGetPackages - the file is missing here
• https://api.nuget.org/v3/index.json - the nuget.org server is suitable for open source products so the paid Telerik assemblies are not available on it
• https://nuget.telerik.com/nuget - this is the legacy Telerik NuGet server which is now deprecated. Make sure to switch to the new Telerik NuGet server -> https://nuget.telerik.com/v3/index.json, which is faster, lighter, and reduces the number of requests from your NuGet client. This will fix the errors and allow you to install the Telerik AJAX controls from a nugget server as explained in this article: First Steps by Installing from a NuGet Package.

Best Regards,
Rumen
Progress Telerik