Hi,
From within IIS:
- Select your site
- Under the IIS header on the site's properties page, open "Authentication"
- Click the "Anonymous Authentication" item
- Click the "Edit" link in the Actions pane.
- Ensure "Application pool identity" is chosen.
If that is set already, you need to double-check your permissions. Not being able to clear the log is always a permissions issue. IIS defaults websites to use the "IUSR" user as the anonymous identity but when we harden our servers, as we should, by setting the folder/file permissions to use the Application Pool Identity, things like this can break.
Hope this helps,
Joe