Why access denied error on this

I am getting this below error, however I have added IUSR_Machinname and given read/write acces on Windows Explorer, still this error, any help is appreciated. Thasnks for any help
Access to the path 'd:\Webs\sos\www\wms\Docs\1000XMLFile.xml' is denied. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.UnauthorizedAccessException: Access to the path 'd:\Webs\sos\www\wms\Docs\1000XMLFile.xml' is denied. ASP.NET is not authorized to access the requested resource. Consider granting access rights to the resource to the ASP.NET request identity. ASP.NET has a base process identity (typically {MACHINE}\ASPNET on IIS ...