The Windows Process Activation Service failed to generate an application pool config file for application pool 'SecurityTokenApplicationPool'. The error type is '7'. To resolve this issue please ensure that the applicationhost.config file is correct and recommit the last configuration chnages made. The data field contains the error number.
According to T734988, in order to troubleshoot this event you need to check the IIS configuration integrity. After you make changes to the ApplicationHost.config file, you can verify its integrity by testing it with Appcmd.exe. If the test fails, note the error, then backup the ApplicationHost.config file and change the ApplicationHost.config file based on the error you noted in the previous steps. Please see the article for full details.
From a support forum:
If you have problem with IIS then please check the Applicationhost.config file was backup and restore from backup (IIS automatically backup the config, if you modify the applicationhost.config)
Check the backup:
%systemroot%\system32\inetsrv\appcmd list backup
%systemroot%\system32\inetsrv\appcmd add backup
%systemroot%\system32\inetsrv\appcmd restore backup "CFGHISTORY_0000000000"
From a support forum: "We got this error after installing the Microsoft .Net 1.1 Framework when .Net 4.0 was already installed. After reinstalling .Net 4.0 the error dissapeared."
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