cant update to new wordpress – php warning

hi
i just tried to update my really old site but no luck: i get this error message:

Warning: Illegal string offset ‘total_users’ in /home/michalmi/public_html/projektcelebrita/wp-includes/update.php on line 67

i understand this is some syntax error but my php skills are really poor… any suggestions? here is the problematic bit of the php document:

$query = array(
‘version’ => $wp_version,
‘php’ => $php_version,
‘locale’ => $locale,
‘mysql’ => $mysql_version,
‘local_package’ => isset( $wp_local_package ) ? $wp_local_package : ”,
‘blogs’ => $num_blogs,
‘users’ => $user_count[‘total_users’],
‘multisite_enabled’ => $multisite_enabled
);

$url = ‘https://api.www.ads-software.com/core/version-check/1.6/?’ . http_build_query( $query, null, ‘&’ );

any ideas?
thanks a lot