Try using a wrapper as suggested in the Mason manual, for example:

#!/usr/bin/perl
# handler.pl

package HTML::Mason;

use HTML::Mason;
use HTML::Mason::ApacheHandler;
use strict;

{
  package HTML::Mason::Commands;
  use DBI ();
  use CGI ();
}

DBI->install_driver('mysql');
CGI->compile(':standard');

my $ah = HTML::Mason::ApacheHandler->new( 
  comp_root => '/path/to/comp/root',
  data_dir  => '/path/to/data/dir'
);

sub handler {
  my ($r) = @_;   
  return $ah->handle_request($r);
}

1;
[download]

Load it from httpd.conf:

PerlRequire /path/to/handler.pl
[download]

Speaking of httpd.conf, here's part of yours:

> KeepAlive On
> ...
> MaxClients 150

You should configure apache properly for mod_perl. Generally you want keepalive turned off and maxclients set to something your server can handle based on the size of your apache children.