Windows Process Activation Service (WAS) encountered a failure when it started a worker process to serve the application pool

If your application pool is running under a specific identity, an expired password could be the cause for your problem.

I had similar problems, see http://blog.janjonas.net/2012-07-14/iis_75-fix-application-pool-disabled-windows-process-activation-service-failure-worker-process-event-id-5059

In IIS, go to Application Pools, and check the Identity of your Application Pool.

Is the App Pool using a custom account? Does it need to be?

Try changing the Identify to a Built-in account like ApplicationPoolIndentity. To do this, go to Advanced Settings, Process Model, Identity. Remember to restart the App Pool after making your changes.

Check that the account or group has the "Log on as Batch Job" permission checked. To change this policy on a domain controller perform the following steps:

• Start>Run gpmc.msc - edit
• Select Forest>Domains>Domain Name> Domain Controller
  • Right click on "Default Domain Policy" and choose edit
• Next edit:
  • Computer Configuration>Policies>Windows Settings>Security Settings>Local Policies>User Rights assignment
• Add user or group to "Log on as Batch Job"
  • Check group membership of service account (in Active Directory) if a particular group is being used for this purpose.
• From the command prompt run "gpupdate /force"

Note: This is a resolution for the problem with SharePoint 2010.

I did the below steps.

1. Windows+R open Run and type services.msc
2. search for Windows Process Activation Service and start the service for me it was stopped.
3. Windows+R type inetmgr.
4. restart all the App pool.
5. Try to start the website under Sites, if it gives an error saying cant start the service because of The World Wide Web Publishing service is stopped.
6. repeat step 1.
7. search for World Wide Web Publishing service, and restart the service.

In my case: I already see the application pool running with right Identity, but I still see the "WAS encountered a failure...". So, I set the same Identity again by re-adding the user in Advance Settings --> Identity --> Custom Account, restarted IIS and it worked!