I replaced this part:
#
#-----[ OPEN ]------------------------------------------------
#
privmsg.php
#
#-----[ FIND ]------------------------------------------------
#
$to_username = phpbb_clean_username($HTTP_POST_VARS['username']);
#
#-----[ REPLACE WITH ]----------------------------------------
#
// Start replacement - Custom mass PM MOD
$to_username_array = explode (";", $HTTP_POST_VARS['username']);
sort ($to_username_array);
foreach ($to_username_array as $name) $to_usernames .= "'".htmlspecialchars(trim($name))."',";
$to_usernames[strlen($to_usernames)-1]=" ";
// End replacement - Custom mass PM MOD
That ssems to work and EasyMod goes through