title: ASP.NET Core hard crash after upgrade to Microsoft.NETCore.App
body: <p>I have an IdentityServer4 application which has been around for a while. It has been upgraded to .NET Core 2.2 a while ago however i noticed that it was still using </p>
  
  <pre><code>Microsoft.AspNetCore.All
  </code></pre>
  
  <p>I am trying to upgrade all of the dlls including this one and move to </p>
  
  <pre><code>Microsoft.NETCore.App 
  Microsoft.AspNetCore.App 
  </code></pre>
  
  <p>When I try to run this localhost on my machine.  The application does compile but it crashes hard.  There is nothing in the log it does not hit program.cs <code>main()</code> or startup.cs.   It just dies.</p>
  
  <p>I can see this in the windows event log </p>
  
  <blockquote>
    <p>Application '/LM/W3SVC/2/ROOT' with physical root 'C:\Development\identityserver\src\IdentityServer\' failed to start process with commandline 'c:\program files (x86)\microsoft visual studio\2017\professional\common7\ide\extensions\microsoft\web tools\projectsystem\VSIISExeLauncher.exe -argFile "C:\Users\ll\AppData\Local\Temp\tmp88E7.tmp"' with multiple retries. The last try of listening port is '36399'. See previous warnings for details.</p>
  </blockquote>
  
  <p>with an event id of 1020</p>
  
  <p>if i Google that event id I get <a href="https://social.technet.microsoft.com/Forums/ie/en-US/581e86b0-a163-46dc-b408-7936cb938484/dhcp-scope-full-event-id-1020?forum=winserveripamdhcpdns" rel="nofollow noreferrer">DHCP scope full, event ID 1020</a></p>
  
  <p>I have no idea how this could have anything to do with a DHCP server running on my local machine.  </p>
  
  <p>Which lead me to this <a href="https://docs.microsoft.com/en-us/aspnet/core/fundamentals/servers/kestrel?view=aspnetcore-2.2#transport-configuration" rel="nofollow noreferrer">Transport configuration</a>  So i added  <code>UseLibuv()</code>  which did not help its still crashing with the same error.</p>
  
  <p>What have I missed?</p>