Custom provider settings are missing

I made a custom provider based on this article:

http://www.iis.net/learn/extensions/url-rewrite-module/developing-a-custom-rewrite-provider-for-url-rewrite-module

It was added to the GAC, it even shows up in IIS manager, but when i try to add settings none of them show in the dropdown.

I triple checked everything, i can't see anything wrong with the code. I'm using Server 2008R2 with IIS 7.5 and .NET 3.5

Any ideas?