This error occurs on systems where the global setting prevents a website from setting this value. To fix

1. Go to your applicationHost.config - usually located in 
   %windir%\system32\inetsrv\config\applicationHost.config  
2. somewhere around line 62 you'll find this: 
   <section name="handlers" overrideModeDefault="Deny" />  
3. Change that to this
   <section name="handlers" overrideModeDefault="Allow" />

that's it :)