.htaccess for forum subdirectory of web not working

[IzFazt]

In the web dir there is the working .htaccess for Drupal which I obtained from this forum. There is a subdirectory called forum which has the phpBB SEO version installed. When I activate URL rewriting for phpBB in the forum directory, it says 404 not found for every url and jumps to the root because of other settings for 404 not found. Below is my .htaccess can somebody tell what is wrong?

# Lines That should already be in your .htacess
<Files "config.php">
Order Allow,Deny
Deny from All
</Files>
<Files "common.php">
Order Allow,Deny
Deny from All
</Files>

# You may need to un-comment the following lines
# Options +FollowSymlinks
# To make sure that rewritten dir or file (/|.html) will not load dir.php in case it exist
# Options -MultiViews
# REMEBER YOU ONLY NEED TO STARD MOD REWRITE ONCE
RewriteEngine On
# REWRITE BASE
RewriteBase /
# HERE IS A GOOD PLACE TO FORCE CANONICAL DOMAIN
# RewriteCond %{HTTP_HOST} !^1nd\.discounthost\.biz$ [NC]
# RewriteRule ^(.*)$ http://1nd.discounthost.biz/$1 [QSA,L,R=301]

# DO NOT GO FURTHER IF THE REQUESTED FILE / DIR DOES EXISTS
RewriteCond %{REQUEST_FILENAME} -f
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
################################################## ###
# PHPBB SEO REWRITE RULES ALL MODES
################################################## ###
# AUTHOR : dcz www.phpbb-seo.com
# STARTED : 01/2006
#################################
# FORUMS PAGES
###############
# FORUM INDEX REWRITERULE WOULD STAND HERE IF USED. "forum" REQUIRES TO BE SET AS FORUM INDEX
# RewriteRule ^forum/forum\.html$ /forum/index.php [QSA,L,NC]
# FORUM ALL MODES
RewriteRule ^forum/(forum|[a-z0-9_-]*-f)([0-9]+)(-([0-9]+))?\.html$ /forum/viewforum.php?f=$2&start=$4 [QSA,L,NC]
# TOPIC WITH VIRTUAL FOLDER ALL MODES
RewriteRule ^forum/(forum|[a-z0-9_-]*-f)([0-9]+)/(topic|[a-z0-9_-]*-t)([0-9]+)(-([0-9]+))?\.html$ /forum/viewtopic.php?f=$2&t=$4&start=$6 [QSA,L,NC]
# GLOBAL ANNOUNCES WITH VIRTUAL FOLDER ALL MODES
RewriteRule ^forum/announces/(topic|[a-z0-9_-]*-t)([0-9]+)(-([0-9]+))?\.html$ /forum/viewtopic.php?t=$2&start=$4 [QSA,L,NC]
# TOPIC WITHOUT FORUM ID & DELIM ALL MODES
RewriteRule ^forum/([a-z0-9_-]*)/?(topic|[a-z0-9_-]*-t)([0-9]+)(-([0-9]+))?\.html$ /forum/viewtopic.php?forum_uri=$1&t=$3&start=$5 [QSA,L,NC]
# PHPBB FILES ALL MODES
RewriteRule ^forum/resources/[a-z0-9_-]+/(thumb/)?([0-9]+)$ /forum/download/file.php?id=$2&t=$1 [QSA,L,NC]
# PROFILES ALL MODES WITH ID
RewriteRule ^forum/(member|[a-z0-9_-]*-u)([0-9]+)\.html$ /forum/memberlist.php?mode=viewprofile&u=$2 [QSA,L,NC]
# USER MESSAGES ALL MODES WITH ID
RewriteRule ^forum/(member|[a-z0-9_-]*-u)([0-9]+)-(topics|posts)(-([0-9]+))?\.html$ /forum/search.php?author_id=$2&sr=$3&start=$5 [QSA,L,NC]
# GROUPS ALL MODES
RewriteRule ^forum/(group|[a-z0-9_-]*-g)([0-9]+)(-([0-9]+))?\.html$ /forum/memberlist.php?mode=group&g=$2&start=$4 [QSA,L,NC]
# POST
RewriteRule ^forum/post([0-9]+)\.html$ /forum/viewtopic.php?p=$1 [QSA,L,NC]
# ACTIVE TOPICS
RewriteRule ^forum/active-topics(-([0-9]+))?\.html$ /forum/search.php?search_id=active_topics&start=$2&sr=top ics [QSA,L,NC]
# UNANSWERED TOPICS
RewriteRule ^forum/unanswered(-([0-9]+))?\.html$ /forum/search.php?search_id=unanswered&start=$2&sr=topics [QSA,L,NC]
# NEW POSTS
RewriteRule ^forum/newposts(-([0-9]+))?\.html$ /forum/search.php?search_id=newposts&start=$2&sr=topics [QSA,L,NC]
# THE TEAM
RewriteRule ^forum/the-team\.html$ /forum/memberlist.php?mode=leaders [QSA,L,NC]
# HERE IS A GOOD PLACE TO ADD OTHER PHPBB RELATED REWRITERULES

# FORUM WITHOUT ID & DELIM ALL MODES (SAME DELIM)
# THESE FOUR LINES MUST BE LOCATED AT THE END OF YOUR HTACCESS TO WORK PROPERLY
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^forum/([a-z0-9_-]+)(-([0-9]+))\.html$ /forum/viewforum.php?forum_uri=$1&start=$3 [QSA,L,NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^forum/([a-z0-9_-]+)\.html$ /forum/viewforum.php?forum_uri=$1 [QSA,L,NC]
# END PHPBB PAGES
################################################## ###

[till]

I guess you have to change the line:

RewriteBase /

to:

RewriteBase /forum/

as your forum is not in the web root directory.

[IzFazt]

tnx for your quick reply, I tried it but it doesnt solve it. In fact also phpBB SEO should have put it automaticly to /forum/ when creatinq this .htaccess file during setup. Normally it does. Somewhere in the environment it doesn't recognise being in a subdir nor does the system obey this .htaccess when changed to /forum/