title: A process serving application pool 'Classic .NET AppPool' suffered a fatal communication error with the Windows Process Activation Service
body: <p>I am running an ASP.NET 3.5 web application on IIS 7 on Windows Server 2008.</p>
  
  <p>I received the following error earlier this afternoon:</p>
  
  <p><code>HTTP Error 503. The service is unavailable.</code></p>
  
  <p>I looked in the Event logs and discovered that:</p>
  
  <p><code>A process serving application pool 'Classic .NET AppPool' suffered a fatal communication error with the Windows Process Activation Service. The process id was '3328'. The data field contains the error number.</code></p>
  
  <p>Here is the full details of that event:</p>
  
  <pre><code>Log Name:      System
  Source:        Microsoft-Windows-WAS
  Date:          18/09/2009 14:58:31
  Event ID:      5011
  Task Category: None
  Level:         Warning
  Keywords:      Classic
  User:          N/A
  Computer:      computername
  Description:
  A process serving application pool 'Classic .NET AppPool' suffered a fatal communication error with the Windows Process Activation Service. The process id was '3328'. The data field contains the error number.
  Event Xml:
  &lt;Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"&gt;
    &lt;System&gt;
      &lt;Provider Name="Microsoft-Windows-WAS" Guid="{5 .. 0}" EventSourceName="WAS" /&gt;
      &lt;EventID Qualifiers="32768"&gt;5011&lt;/EventID&gt;
      &lt;Version&gt;0&lt;/Version&gt;
      &lt;Level&gt;3&lt;/Level&gt;
      &lt;Task&gt;0&lt;/Task&gt;
      &lt;Opcode&gt;0&lt;/Opcode&gt;
      &lt;Keywords&gt;0x80000000000000&lt;/Keywords&gt;
      &lt;TimeCreated SystemTime="2009-09-18T13:58:31.000Z" /&gt;
      &lt;EventRecordID&gt;23552&lt;/EventRecordID&gt;
      &lt;Correlation /&gt;
      &lt;Execution ProcessID="0" ThreadID="0" /&gt;
      &lt;Channel&gt;System&lt;/Channel&gt;
      &lt;Computer&gt;computername&lt;/Computer&gt;
      &lt;Security /&gt;
    &lt;/System&gt;
    &lt;EventData&gt;
      &lt;Data Name="AppPoolID"&gt;Classic .NET AppPool&lt;/Data&gt;
      &lt;Data Name="ProcessID"&gt;3328&lt;/Data&gt;
      &lt;Binary&gt;6D000780&lt;/Binary&gt;
    &lt;/EventData&gt;
  &lt;/Event&gt;
  </code></pre>
  
  <p>This resulted in:</p>
  
  <p><code>Application pool 'Classic .NET AppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool.</code></p>
  
  <p>Here is the full details of that event:</p>
  
  <pre><code>Log Name:      System
  Source:        Microsoft-Windows-WAS
  Date:          18/09/2009 15:03:05
  Event ID:      5002
  Task Category: None
  Level:         Error
  Keywords:      Classic
  User:          N/A
  Computer:      computername
  Description:
  Application pool 'Classic .NET AppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool.
  Event Xml:
  &lt;Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"&gt;
    &lt;System&gt;
      &lt;Provider Name="Microsoft-Windows-WAS" Guid="{5 .. 0}" EventSourceName="WAS" /&gt;
      &lt;EventID Qualifiers="49152"&gt;5002&lt;/EventID&gt;
      &lt;Version&gt;0&lt;/Version&gt;
      &lt;Level&gt;2&lt;/Level&gt;
      &lt;Task&gt;0&lt;/Task&gt;
      &lt;Opcode&gt;0&lt;/Opcode&gt;
      &lt;Keywords&gt;0x80000000000000&lt;/Keywords&gt;
      &lt;TimeCreated SystemTime="2009-09-18T14:03:05.000Z" /&gt;
      &lt;EventRecordID&gt;23557&lt;/EventRecordID&gt;
      &lt;Correlation /&gt;
      &lt;Execution ProcessID="0" ThreadID="0" /&gt;
      &lt;Channel&gt;System&lt;/Channel&gt;
      &lt;Computer&gt;computername&lt;/Computer&gt;
      &lt;Security /&gt;
    &lt;/System&gt;
    &lt;EventData&gt;
      &lt;Data Name="AppPoolID"&gt;Classic .NET AppPool&lt;/Data&gt;
      &lt;Binary&gt;
      &lt;/Binary&gt;
    &lt;/EventData&gt;
  &lt;/Event&gt;
  </code></pre>
  
  <p>Concluding in the: HTTP Error 503. The service is unavailable.</p>
  
  <p>Would someone please help me to identify how this happened and what I need to do to prevent it from happening in the future.</p>