camposomar did not say exactly what the incorrect permissions were, but here are the permissions and ownerships that should be set on the files in the /usr/local/cpanel/base/frontend/x3/mail/ directory:
Code:
# ls -alh /usr/local/cpanel/base/frontend/x3mail
total 244K
drwxr-xr-x 8 root root 4.0K Jun 1 22:00 ./
drwxr-xr-x 8 root root 4.0K Aug 12 2008 ../
lrwxrwxrwx 1 root root 14 Dec 17 2008 autodir -> ../x3/autodir//
drwxr-xr-x 15 root root 12K Jun 1 22:00 branding/
-rw-r--r-- 1 root root 464 Jun 5 2007 branding.conf
lrwxrwxrwx 1 root root 18 May 30 2008 charset.html -> ../x3/charset.html
drwxr-xr-x 2 root root 4.0K Dec 16 2009 contact/
-rw-r--r-- 1 root root 322 Jun 5 2007 cpanelplugins.conf
-rw-r--r-- 1 root root 69K Jun 1 22:00 .cpanelsync
-rw-r--r-- 1 root root 26K Jun 1 22:00 .cpanelsync.md5s
-rw-r--r-- 1 root root 1.9K Jun 1 22:00 .cpanelsync.new
lrwxrwxrwx 1 root root 9 May 30 2008 css -> ../x3/css/
lrwxrwxrwx 1 root root 15 Dec 16 2009 css2-min -> ../x3/css2-min//
lrwxrwxrwx 1 root root 16 May 30 2008 dynamicui -> ../x3/dynamicui//
-rw-r--r-- 1 root root 12K Aug 25 21:53 dynamicui.conf
lrwxrwxrwx 1 root root 15 May 30 2008 expander -> ../x3/expander//
lrwxrwxrwx 1 root root 28 Dec 16 2009 extended_statsbar.html -> ../x3/extended_statsbar.html
lrwxrwxrwx 1 root root 33 Dec 16 2009 extended_stats_disable.html -> ../x3/extended_stats_disable.html
lrwxrwxrwx 1 root root 32 Dec 16 2009 extended_stats_enable.html -> ../x3/extended_stats_enable.html
lrwxrwxrwx 1 root root 38 Oct 9 2009 fantastico -> /usr/local/cpanel/3rdparty/fantastico//
drwxr-xr-x 2 root root 4.0K Feb 17 2010 getstarted/
lrwxrwxrwx 1 root root 10 Dec 17 2008 help -> ../x3/help/
lrwxrwxrwx 1 root root 23 May 30 2008 hidegraphics.html -> ../x3/hidegraphics.html
lrwxrwxrwx 1 root root 20 May 30 2008 hideicons.html -> ../x3/hideicons.html
lrwxrwxrwx 1 root root 13 May 30 2008 images -> ../x3/images//
-rw-r--r-- 1 root root 75 Dec 17 2008 index.html
lrwxrwxrwx 1 root root 8 May 30 2008 js -> ../x3/js/
lrwxrwxrwx 1 root root 13 Dec 16 2009 js2-min -> ../x3/js2-min/
drwxr-xr-x 2 root root 4.0K May 30 2008 lang/
drwxr-xr-x 2 root root 4.0K Dec 22 2009 langcss/
lrwxrwxrwx 1 root root 17 May 30 2008 logout.html -> ../x3/logout.html
lrwxrwxrwx 1 root root 10 Dec 17 2008 mail -> ../x3/mail/
lrwxrwxrwx 1 root root 15 May 30 2008 mainicons -> ../x/mainicons//
lrwxrwxrwx 1 root root 15 May 30 2008 nvget.xml -> ../x3/nvget.xml
lrwxrwxrwx 1 root root 18 May 30 2008 nvsetall.xml -> ../x3/nvsetall.xml
lrwxrwxrwx 1 root root 15 May 30 2008 nvset.xml -> ../x3/nvset.xml
lrwxrwxrwx 1 root root 13 May 30 2008 passbar -> ../x3/passbar/
lrwxrwxrwx 1 root root 13 May 30 2008 passwd -> ../x3/passwd//
-rw-r--r-- 1 root root 60K Jun 5 2007 preview.jpg
lrwxrwxrwx 1 root root 16 May 30 2008 resellers -> ../x3/resellers//
lrwxrwxrwx 1 root root 14 May 30 2008 security -> ../x3/security/
lrwxrwxrwx 1 root root 14 May 30 2008 setlang -> ../x3/setlang//
drwxr-xr-x 2 root root 4.0K May 30 2008 shortcuts/
lrwxrwxrwx 1 root root 23 May 30 2008 showgraphics.html -> ../x3/showgraphics.html
lrwxrwxrwx 1 root root 20 May 30 2008 showicons.html -> ../x3/showicons.html
lrwxrwxrwx 1 root root 17 May 30 2008 status.html -> ../x3/status.html
lrwxrwxrwx 1 root root 21 May 30 2008 stdbheader.html -> ../x3/stdbheader.html
lrwxrwxrwx 1 root root 12 May 30 2008 style -> ../x3/style//
lrwxrwxrwx 1 root root 24 Dec 17 2008 switchaccount.html -> ../x3/switchaccount.html
lrwxrwxrwx 1 root root 22 Dec 17 2008 switchtheme.html -> ../x3/switchtheme.html
lrwxrwxrwx 1 root root 21 Dec 16 2009 trademarks.html -> ../x3/trademarks.html
lrwxrwxrwx 1 root root 19 May 30 2008 tutorial.html -> ../x3/tutorial.html
-rw-r--r-- 1 root root 880 Dec 17 2008 update_branding.pl
lrwxrwxrwx 1 root root 33 Dec 16 2009 video_tutorial_include.html -> ../x3/video_tutorial_include.html
lrwxrwxrwx 1 root root 23 May 30 2008 webmaillogin.html -> ../x3/webmaillogin.html
-rw-r--r-- 1 root root 20 Jun 5 2007 Xver
lrwxrwxrwx 1 root root 9 May 30 2008 yui -> ../x3/yui/
camposomar did say that the problem was caused by incorrect permissions on /usr/local/cpanel/base/frontend/x3/mail/fwds.html, so hopefully the directory listing from a known-working server may be helpful.