Archive: rewrited urls get redirected to index.php instead of showing the thread

[Dontom]

Hello,
I modified archive/index.php in order to generate friendlier urls for threads.
Example:

old url:
http://www.rennrad-news.de/forum/archive/index.php/t-886.html

new:
http://www.rennrad-news.de/forum/archive/zugvogel-marathon-am-1-mai-886/

I added the neccessary rewrite rule. When I clik the above Link I get redirected to index.php out instead of the thread I want to get displayed.

Any idea what might cause this in archive/index.php?

Thanks
Thomas