Open the config file and search for "<authorization>". Check if there is another section for this with that same <add accessType=...> line in another location of the config file (other than line 935). The section location would be something like:
<configuration>
<system.webServer>
...
<security>
...
<authorization>
<add accessType="Allow" users="" roles="Administrators" />
</authorization>
</security>
</system.webServer>
</configuration>
If line 935 is under a location tag (<location path="Site">), then this setting may be set at a higher level, such as the server level. If this is the case, try removing line 935. If this works, you may have a delegation issue, and this page might provide some good example for what the configuration should look like: http://learn.iis.net/page.aspx/156/understanding-iis-70-configuration-delegation/