ApplicationPoolIdentity where are you?
ApplicationPoolIdentity is the default username you see assigned to an application pool in IIS 7.x. The only trouble with it is that Windows can’t find it when you try to assign permissions to it, such as when you want to read some files in a folder outside of your website.
Open up the Properties dialog on a folder or file and try to add ApplicationPoolIdentity to the user list on the Security tab. Ain’t gonna happen, Windows can’t find it.
But do not despair, dear reader, the answer is given here: How to assign permissions to ApplicationPoolIdentity account.
The short version: use the name “IIS APPPOOL\DefaultAppPool” and Windows will find it.
It works – I just tried it.
Hope that helps.