Fatal error: Call to undefined function get

<?php
if (version_compare(PHP_VERSION, '5.0.0.', '<'))
{
die("WP Robot requires php 5 or a greater version to work.");
}
if (!defined('WP_CONTENT_URL'))
{define('WP_CONTENT_URL', get_option('siteurl') . '/wp-content');}
Ps no se xD, tendría que ver el source para ver como esta construido. Pero el problema esta en el porque no puedes llamar esa función, si esta dentro del archivo wp-includes/functions.php

Edit:
Código
274	
275	/**
276	 * Retrieve option value based on name of option.
277	 *
278	 * If the option does not exist or does not have a value, then the return value
279	 * will be false. This is useful to check whether you need to install an option
280	 * and is commonly used during installation of plugin options and to test
281	 * whether upgrading is required.
282	 *
283	 * If the option was serialized then it will be unserialized when it is returned.
284	 *
285	 * @since 1.5.0
286	 * @package WordPress
287	 * @subpackage Option
288	 * @uses apply_filters() Calls 'pre_option_$option' before checking the option.
289	 *      Any value other than false will "short-circuit" the retrieval of the option
290	 *      and return the returned value. You should not try to override special options,
291	 *      but you will not be prevented from doing so.
292	 * @uses apply_filters() Calls 'option_$option', after checking the option, with
293	 *      the option value.
294	 *
295	 * @param string $option Name of option to retrieve. Expected to not be SQL-escaped.
296	 * @return mixed Value set for the option.
297	 */
298	function get_option( $option, $default = false ) {
299	        global $wpdb;
300	
301	        // Allow plugins to short-circuit options.
302	        $pre = apply_filters( 'pre_option_' . $option, false );
303	        if ( false !== $pre )
304	                return $pre;
305	
306	        $option = trim($option);
307	        if ( empty($option) )
308	                return false;
309	
310	        if ( defined( 'WP_SETUP_CONFIG' ) )
311	                return false;
312	
313	        if ( ! defined( 'WP_INSTALLING' ) ) {
314	                // prevent non-existent options from triggering multiple queries
315	                $notoptions = wp_cache_get( 'notoptions', 'options' );
316	                if ( isset( $notoptions[$option] ) )
317	                        return $default;
318	
319	                $alloptions = wp_load_alloptions();
320	
321	                if ( isset( $alloptions[$option] ) ) {
322	                        $value = $alloptions[$option];
323	                } else {
324	                        $value = wp_cache_get( $option, 'options' );
325	
326	                        if ( false === $value ) {
327	                                $row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
328	
329	                                // Has to be get_row instead of get_var because of funkiness with 0, false, null values
330	                                if ( is_object( $row ) ) {
331	                                        $value = $row->option_value;
332	                                        wp_cache_add( $option, $value, 'options' );
333	                                } else { // option does not exist, so we must cache its non-existence
334	                                        $notoptions[$option] = true;
335	                                        wp_cache_set( 'notoptions', $notoptions, 'options' );
336	                                        return $default;
337	                                }
338	                        }
339	                }
340	        } else {
341	                $suppress = $wpdb->suppress_errors();
342	                $row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
343	                $wpdb->suppress_errors( $suppress );
344	                if ( is_object( $row ) )
345	                        $value = $row->option_value;
346	                else
347	                        return $default;
348	        }
349	
350	        // If home is not set use siteurl.
351	        if ( 'home' == $option && '' == $value )
352	                return get_option( 'siteurl' );
353	
354	        if ( in_array( $option, array('siteurl', 'home', 'category_base', 'tag_base') ) )
355	                $value = untrailingslashit( $value );
356	
357	        return apply_filters( 'option_' . $option, maybe_unserialize( $value ) );
358	}