Hello,

The behavior you described can happen if old local NuGet package source entries for previous Telerik UI for Blazor versions remain in your nuget.config after updating. This is common when using the Product Updater or Visual Studio's update prompts, as these tools may add new package sources but not automatically remove outdated ones.

Why this happens:

• The Product Updater and Visual Studio may add new package source entries for updated versions but do not clean up old entries.
• Multiple local feeds referencing different versions can confuse NuGet and cause restore/build failures.

How to resolve:

• Open your nuget.config file (usually found at the solution root or project directory).
• Remove any <packageSources> entries pointing to old Telerik UI for Blazor local feeds. Keep only the latest version or the official Telerik NuGet feed:

  <packageSources>
    <add key="Telerik" value="https://nuget.telerik.com/v3/index.json" />
  </packageSources>
  

• Save the file.
• Clear your local NuGet cache and restore packages:

  dotnet nuget locals all --clear
  dotnet restore
  

I would wecommend you to use Telerik Blazor Upgrade Wizard to upgrade the version of existing Telerik UI for Blazor app.

It will replace the older version with the latest version and your proj file would look similar to:

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>net10.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <BlazorDisableThrowNavigationException>true</BlazorDisableThrowNavigationException>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Telerik.UI.for.Blazor">
      <Version>13.3.0</Version>
    </PackageReference>
  </ItemGroup>
</Project>

Preventative measures:

• Before updating, check your nuget.config for old entries and remove them manually.

Questions for clarification:

• Is your nuget.config located at the solution root, or do you have multiple configs in subfolders? If so, the issue might persist across configs.
• Are you using the online Telerik NuGet feed or local feeds for package restores?

References:

• Setting up the Telerik NuGet feed:
  • https://docs.telerik.com/blazor-ui/installation/nuget
• NuGet feed configuration in Visual Studio:
  • https://docs.telerik.com/blazor-ui/installation/automated#set-up-a-local-nuget-feed-in-visual-studio

Best Regards,

Misho
Progress Telerik