There is no GUI available in the SharePoint Central Administration website to delete a SharePoint 2010 application pool.
Deleting the application pool from the Internet Information Services (IIS) manager is also not helping as you will still get the error when trying to create a new application pool with the same name.
The only way is to delete the application pool entry from SharePoint is via PowerShell command.
Here are the steps:
- Launch the SharePoint 2010 Management Shell with administrator privileges
(Start -> All Programs -> Microsoft SharePoint 2010 Products -> Right click on SharePoint 2010 Management Shell -> Run as administrator)
- Run 'Get-SPServiceApplicationPool'
- Run 'Get-SPServiceApplicationPool -Identity <Name of the application pool>'
- Run ‘Remove-SPServiceApplicationPool’
- Input the Identity <name of the application pool>
- Input 'Y' to delete the application pool