How to get rid off the error 500 while using the IpSecurity in the Web.config

This is what I have in the folder that I want to protect from unauthorized users.
I only want that the user IP while logged on to my ASP.NET app has access to the files located in the folder {articles/}


 
 
 
 
 
 
 
 
 
   
 
 

But instead of getting an error 403 I get the error 500 the hosting environment is win 2008 IIS7.

Does any one have an idea how to fix this issue?

Thanks