I've just installed the latest version again.
it seems you didn't switch on the $mod_rewrite setting of setup_options.php. Make sure it's set to TRUE and is not slashed.
From the Manual:
When you are sure that mod_rewrite module is set up correctly on your server, you need to create .htaccess file and put under the forums folder. It should look like this:
RewriteRule ^index\.html$ ./index.php?mdrw=on
RewriteRule ^manual\.html$ ./index.php?action=manual&mdrw=on
RewriteRule ^([0-9]+)_([0-9]+)_([-0-9]+)\.html$ ./index.php?action=vthread&forum=$1&topic=$2&page=$3&mdrw=on
RewriteRule ^([0-9]+)_([-0-9]+)\.html$ ./index.php?action=vtopic&forum=$1&page=$2&mdrw=on
The PageNav on the first Forumssite will link to ../forums/2/ with an 404 Error. On the Topicsite the PageNav link to .../forums/6_2.html and works perfectly.
The htaccess must be adapted to the following line:
RewriteRule ^([0-9]+)/$ ./index.php?page=$1&mdrw=on
After that everything works perfectly. The Installation Guide should be adjusted accordingly? Or I myself have not read anything properly ;-)
Arrrrggggg .... i see the Problem :)
Look at the Online Manual: Most Recently updated on March 25, 2010. And now look in your Manual under /templates .. Most Recently updated on December 15, 2011! Small problem with a big impact
Problem identified, problem solved. You all have a nice day.