Substatus Error Codes in Log Files (IIS 6.0)
When enabled, substatus error codes are written to IIS log files whenever a client request fails.
You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /user:Administrative_AccountName "mmc %systemroot%\system32\inetsrv\iis.msc".
To log substatus error codes