The one thing you dread seeing…Azure DevOps [Build failed]

For the last few hours I have been trying to sort a problem with a build that started failing out of the blue. The solution compiled and ran locally with success and previous pipeline builds completed successfully.

Azure DevOps Build Failed Message

The build was suddenly complaining about the project.assets.json file and that I had to run a NuGet package restore which would create the file for me.

I already had a NuGet Restore step in my pipeline, so what was the problem? Why wasn’t it restoring the files?

In an attempt to force the restore, I added a /t:restore parameter to the MSBuild task. I could see that the NuGet feeds were being interogated and files downloaded and installed, but it would fail trying to restore a package from the Telerik NuGet feed. Strange, as running a restore locally worked OK.

Checking one of the projects I could see that a Telerik package had an update available and it did relate to the project that was having the problem. I upgraded the package and checked the solution back in to kick off the build pipeline. It subsequently failed again with the same problem!

During my investigation, I noticed that our Hosted Agent was set to VS2017, which has since been deprecated.

Best to change that.

I changed the Agent Pool to Azure Pipelines and set the Agent Specification to windows-2019

Azure DevOps Agent Pool

You can see a list of the available virtual machine images here (Agent Specifications) here.

I also removed the /t:restore parameter from the MSBuild task that I previously added. I was certain this wasn’t the problem.

Saving and queuing up a new build, I waited for the MSBuild task to complete.


I suspect the problem was down to the local NuGet package cache on the Virtual Agent needing a bit of a kick.

If anyone else comes across the problem, I hope this helps.

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