Here is it:

HEAD /aprunasimies/forums/forum.php?id=2%23page-1 HTTP/1.1
User-Agent: User-Agent
If-Modified-Since: Mozilla/4.0 (compatible; Windows XP 5.1)

%23 is a # character (must not be in the URL sent to the server). User agent is fun and If-Modified-Since is even more fun...

No wonder that it is blocked.

The Internet is full of junk :(