I'm guessing that you are using a web.config file instead of .htaccess to perform the URL mapping, since your server is running IIS rather than Apache.
The problem will be in this file, where it is not translating special characters correctly into the query parameter. Sadly I don't have any experience in configuring IIS, so perhaps someone else can help with this issue.
Also, out of curiosity, does your 'Admin' panel show 'OK' by the form of URL structure that you chose?