Problem with Custom xHTML function

I have created and tested a custom theme I made for the Custom xHTML function, and it seem to be running perfectly local with WebMatrix, but when I try the same thing on my website, it just dosent work and shows the original page. I have tested with using the default Custom xHTML files and with the files from the default folder but same problem appears. What can cause the problem?

My solution for now is to copy the custom theme to the default folder and use that function instead, and that works perfect.