foreach doesnt work with IE

[emath]

I made this script : ( in a hook )

PHP Code:

if ($_REQUEST['do'] == 'rqusers' AND $vbulletin->options['active_users_onoff'] AND isset($activeusers) )
{
    $first=true;
    foreach ( $activeusers as $row ) {
        if ( $first )    { 
            $first = false;
            $str = "<li><a class=\"username\" href=\" \"> " . $row["musername"] . "</a></li>";    } 
        else { 
            $str .= ",&nbsp<li><a class=\"username\" href=\" \"> " . $row["musername"] . "</a></li>";    }            
    }    
    echo "<p>" . construct_phrase($vbphrase['users_currently_browsing_x_y_z'], $totalonline, $numberregistered, $numberguest) . "</p><ol class=\"commalist\">" . $str . "</ol>" ;
    exit;
} 


though, on IE, and only IE this doesnt work ( it doesnt through the IF .. )

if i take off the AND isset($activeusers) then i get the error :

Invalid argument supplied for foreach()

any ideas with this ? i tried to do as $key => $value

but it didnt work, again this only happening with IE, with CHROME and FIREFOX everything works great.