problem editing themes in v2.7

problem editing theme directly from v2.7 back end:

ERROR MESSAGE
Warning: fopen(C:\Sites\Single39\ammarcarl\webroot\news/wp-content/themes/black-lucas/style.css) [function.fopen]: failed to open stream: Permission denied in C:\Sites\Single39\ammarcarl\webroot\news\wp-admin\theme-editor.php on line 55

Warning: Cannot modify header information – headers already sent by (output started at C:\Sites\Single39\ammarcarl\webroot\news\wp-admin\theme-editor.php:55) in C:\Sites\Single39\ammarcarl\webroot\news\wp-admin\theme-editor.php on line 70

here’s line 55:

$f = fopen($real_file, ‘w+’);

…which lies within this string:

check_admin_referer(‘edit-theme_’ . $file . $theme);

if ( !current_user_can(‘edit_themes’) )
wp_die(‘<p>’.__(‘You do not have sufficient permissions to edit templates for this blog.’).'</p>’);

$newcontent = stripslashes($_POST[‘newcontent’]);
$theme = urlencode($theme);
if (is_writeable($real_file)) {
//is_writable() not always reliable, check return value. see comments @ https://uk.php.net/is_writable
$f = fopen($real_file, ‘w+’);
if ($f !== FALSE) {
fwrite($f, $newcontent);
fclose($f);
$location = “theme-editor.php?file=$file&theme=$theme&a=te”;
} else {
$location = “theme-editor.php?file=$file&theme=$theme”;
}
} else {
$location = “theme-editor.php?file=$file&theme=$theme”;
}

$location = wp_kses_no_null($location);
$strip = array(‘%0d’, ‘%0a’);
$location = str_replace($strip, ”, $location);
header(“Location: $location”);
exit();

any thoughts on how to fix this?