Check what are the set of Permissions required for the Application pool identity

NTFS permissions

Directory	Users\Groups	Permissions
%windir%\help\iishelp\common	IIS_WPG	Read, execute
%windir%\IIS Temporary Compressed Files	IIS_WPG	Full control
%windir%\system32\inetsrv\ASP compiled templates	IIS_WPG	Full control
Inetpub\wwwroot (or content directories)	IIS_WPG	Read, execute

Registry permissions

Location	Users\Groups	Permissions
HKLM\System\CurrentControlSet\Services\ASP	IIS_WPG	Read
HKLM\System\CurrentControlSet\Services\HTTP	IIS_WPG	Read
HKLM\System\CurrentControlSet\Services\IISAdmin	IIS_WPG	Read
HKLM\System\CurrentControlSet\Services\w3svc	IIS_WPG	Read

Windows user rights

Policy	Users
Access this computer from the network	ASPNET
Access this computer from the network	IWAM_MachineName
Adjust memory quotas for a process	IWAM_MachineName
Adjust memory quotas for a process	Network service
Bypass traverse checking	IIS_WPG
Deny logon locally	ASPNET
Impersonate a client after authentication	ASPNET
Impersonate a client after authentication	IIS_WPG
Log on as a batch job	ASPNET
Log on as a batch job	IIS_WPG
Log on as a batch job	IWAM_MachineName
Logon as a service	ASPNET
Logon as a service	Network service
Replace a process level token	IWAM_MachineName
Replace a process level token	Network service