title: TeamCity Build Agent (v27767) deletes MsBuild.exe on run
body: <p>TeamCity 8.0.6 CI box with build agent has been purring along for several years. After a system restart, TeamCity seems to have auto-upgraded the local build agent to version 27767. No other configuration changes were made, but this error now shows on build trigger:</p>
  
  <pre><code>Unable to find MSBuild at C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe, please check MSBuild environment variable to target to Microsoft .NET Framework 2.0/3.5/4.0 or Mono installation directory
  </code></pre>
  
  <p>I RDP'd into the box and see that MSBuild.exe went missing - strange. So I re-add it from a local install and retrigger a build. As soon as the build agent picks up the file, it disappears! Happens every time. Maybe Windows is protecting this folder?</p>
  
  <p>The build agent then becomes "incompatible". I tried this <a href="https://stackoverflow.com/a/38712136/198927">workaround</a>, but this doesn't stop <code>msbuild.exe</code> from being deleted.</p>
  
  <p>I checked that there are no odd steps in my build configuration. What could be deleting or moving MSBuild?</p>