Down in your bbs_forum.cgi sub "PrintPostOrReplyPage", at the
very end is a line:

     require "bbs_html_create_message.pl";

Replace it with:

     if (-e "$forum_dir/$username.lock") {
         unlink("$forum_dir/$username.lock");
     }
 
     open (LOCKFILE, ">$forum_dir/$username.lock") ||
     &CgiDie("Could Not Open Lock File\n");
     print LOCKFILE "";
     close (LOCKFILE);

     require "bbs_html_create_message.pl";

Down in the sub "CreatePosting", enclose everything in the subroutine with
this "if" statement:

     if (-e "$forum_dir/$username.lock") {
         unlink("$forum_dir/$username.lock");
         ...the rest of the CreatePosting subroutine up until &PrintForumPage
            then...
     } # end of if post file lock exists

     &PrintForumPage;

You just need to make sure the last &PrintForumPage call is the last command
in the subroutine before it returns, so that the system will always run
&PrintForumPage whether it posts a message or not.