Hi dc_duo,
Did you mean the security settings in IIS or the file system? If you just want to create or write to a file using PHP, then the PHP application needs the write permissions on the file system. Please make sure the user account has write permission to both the folder and the file(if the file exists). And here are the accounts that the write permissions should be granted to according to the authentication method:
* The logon user must have permissions when you are using Integrated Windows authentication or Basic authentication.
* The IUSR_MachineName account should have the permissions if the anonymous access is enabled.
However, if you are not certain which account is currently used by your PHP application, you can try the everyone group instead. This should be the simplest solution and can be used to verify the issue.
Hope it helps.