title: Azure DevOps YAML Pipeline fails with "A sequence was not expected"
body: <p>I've been attempting to create a YAML pipeline in Azure DevOps (Version Dev17.M153.3).</p>
  <p>I created a simple Hello World C# console app and checked it into our locally hosted Azure-Git repo. I created my azure-pipelines.yml file and have tried various combinations of things in it including:</p>
  <ul>
  <li>The &quot;.NET Desktop&quot; configuration</li>
  <li>The &quot;Starter Pipeline&quot; configuration</li>
  <li>A file from another C# project that I know works</li>
  <li>A file form another project, with various mods to match my test project</li>
  <li>A completely commented-out file</li>
  <li>A completely blank file</li>
  </ul>
  <p>However, every time I try to do a build, I get the following failure message:</p>
  <blockquote>
  <p>/azure-pipelines.yml (Line: 1, Col: 1): A sequence was not expected</p>
  </blockquote>
  <p>Given the error always occurs on line 1 and I've tried lots of different content in the file, I think something else must be configured incorrectly, rather than a problem with the YAML.</p>
  <p>Does anyone have any ideas what I'm doing wrong, please?
  Various Google searches find pages with similar errors, but none of the solutions helped me.</p>
  <hr />
  <p>*** Edited to add various YAML file attempts:</p>
  <p>I currently have a completely empty YAML file, but still get the error.
  Previous files have included:</p>
  <pre><code>- task: DotNetCoreCLI@2
    inputs:
      command: 'build'
      projects: '.'
  
  ---------------------------------
  
  variables:
    solution: 'HelloWorldCsharpSandpit.sln'
  
  - task: VSBuild@1
    displayName: 'Build solution (debug)'
    inputs:
      solution: '$(solution)'
      vsVersion: 16.0
      platform: x86
      configuration: Debug
      clean: true
    timeoutInMinutes: 10
  
  ---------------------------------
  
  # .NET Desktop
  # Build and run tests for .NET Desktop or Windows classic desktop solutions.
  # Add steps that publish symbols, save build artifacts, and more:
  # [Link removed to avoid odd formatting.]
  
  trigger:
  - master
  
  pool:
    name: 'Default'
  
  variables:
    solution: '**/*.sln'
    buildPlatform: 'Any CPU'
    buildConfiguration: 'Release'
  
  steps:
  - task: NuGetToolInstaller@0
  
  - task: NuGetCommand@2
    inputs:
      restoreSolution: '$(solution)'
  
  - task: VSBuild@1
    inputs:
      solution: '$(solution)'
      platform: '$(buildPlatform)'
      configuration: '$(buildConfiguration)'
  
  - task: VSTest@2
    inputs:
      platform: '$(buildPlatform)'
      configuration: '$(buildConfiguration)'
  
  
  ---------------------------------
  
  # .NET Desktop
  # Build and run tests for .NET Desktop or Windows classic desktop solutions.
  # Add steps that publish symbols, save build artifacts, and more:
  # https://docs.microsoft.com/azure/devops/pipelines/apps/windows/dot-net
  #
  #trigger:
  #- master
  #
  #pool:
  #  name: 'Default'
  #
  #variables:
  #  solution: '**/*.sln'
  #  buildPlatform: 'Any CPU'
  #  buildConfiguration: 'Release'
  #
  #steps:
  #- task: NuGetToolInstaller@0
  #
  #- task: NuGetCommand@2
  #  inputs:
  #    restoreSolution: '$(solution)'
  #
  #- task: VSBuild@1
  #  inputs:
  #    solution: '$(solution)'
  #    platform: '$(buildPlatform)'
  #    configuration: '$(buildConfiguration)'
  #
  #- task: VSTest@2
  #  inputs:
  #    platform: '$(buildPlatform)'
  #    configuration: '$(buildConfiguration)'
  
  
  ---------------------------------
  
  # Starter pipeline
  # Start with a minimal pipeline that you can customize to build and deploy your code.
  # Add steps that build, run tests, deploy, and more:
  # https://aka.ms/yaml
  
  trigger:
  - master
  
  pool:
    vmImage: 'ubuntu-latest'
  
  steps:
  - script: echo Hello, world!
    displayName: 'Run a one-line script'
  
  - script: |
      echo Add other tasks to build, test, and deploy your project.
      echo See https://aka.ms/yaml
    displayName: 'Run a multi-line script'
  </code></pre>