Event ID 5127 — IIS Application Pool Availability

Applies To: Windows Server 2008

Web sites and Web applications depend on the availability of Internet Information Services (IIS) application pools. IIS application pools in turn depend on the Windows Process Activation Service (WAS). If WAS is not running or errors occur during the startup or shutdown of an application pool, Web sites and Web applications may not be available.

Event Details

Product: Internet Information Services
ID: 5127
Source: Microsoft-Windows-WAS
Version: 7.0
Message: A worker process '%2' serving application pool '%1' is no longer trusted by the Windows Process Activation Service, based on ill-formed data the worker process sent to the service. The data field contains the error number.


Check an untrusted worker process

A worker process has sent some data to the Windows Process Activation Service (WAS) that was not expected. User code may be trying to engage in malicious activity in the worker process and may have taken over the communication pipe. For example, user code may be sending a second process ID to WAS for the worker process, or be sending performance counter numbers that are not in the right form. This could be an attempt to create a buffer overrun in WAS.

To resolve this issue, examine the worker process to see whether it contains suspect user code. Check the loaded modules. If ISAPI or third-party modules are running, contact the vendor of the modules for more information.


To perform this procedure, you must have membership in Administrators, or you must have been delegated the appropriate authority.

To verify that an application pool has started:

  1. Click Start, click Control Panel, and then click Administrative Tools.
  2. Right-click Internet Information Services (IIS) Manager and select Run as administrator.
  3. In the Connections pane, expand the server node and select Application Pools.
  4. In Features View, the Status column for the application pool will indicate Started if the application pool has started.

IIS Application Pool Availability

Internet Information Services (IIS) 7.0