Hi there,
Can you show me your .htaccess file?
The only potential issue I see is the fact that you don't have the "page" prefix to your page number, that may confuse the URL matcher, but I want to see your .htaccess file just in case there's any conflicts there
<FilesMatch "\.(ico|jpg|jpeg|png|gif|swf|js)$">
Header set Cache-Control "public"
Header set Expires "Fri, 31 Dec 2017 23:59:59 GMT"
</FilesMatch>
<IfModule mod_rewrite.c>
RewriteEngine On
# If you are having problem with "None Could Be Negotiated" errors in Apache,
uncomment this to turn off MultiViews
# Options -MultiViews
#RewriteBase /forum/
RewriteCond %{HTTP_HOST} !^www.semiwiki.com$ [NC]
RewriteRule ^(.*)$ http://www.semiwiki.com/forum/$1 [L,R=301]
RewriteCond %{REQUEST_URI}
!(admincp/|dbseocp/|modcp/|cron|mobiquo|forumrunner|api\.php|reviewpost/|classifieds/|photopost/)
RewriteRule ^((archive/)?(.*\.php(/.*)?))$ dbseo.php [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}
!/(admincp|dbseocp|modcp|clientscript|cpstyles|images|reviewpost|classifieds|photopost)/
RewriteRule ^(.+)$ dbseo.php [L,QSA]
#RewriteRule ^((urllist|sitemap_).*\.(xml|txt)(\.gz)?)$
vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]
#RewriteCond %{REQUEST_URI} !(admincp/|modcp/|cron|vbseo_sitemap)
#RewriteRule ^((archive/)?(.*\.php(/.*)?))$ vbseo.php [L,QSA]
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{REQUEST_FILENAME} !/(admincp|modcp|clientscript|cpstyles|images)/
#RewriteRule ^(.+)$ vbseo.php [L,QSA]
# to redirect /forums/f8/39840-something.html to
# /showthread.php?t=39840
RewriteRule ^forums/[^/]+/([^-]+)-[^.]+\.html$ /showthread.php?t=$1 [R=301,NC,L,QSA]
# to redirect /forums//showthread.php?t=39840 to
# /showthread.php?t=39840
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^forums/([^/]+)/?$ /$1 [R=301,NC,L]
</IfModule>