Error When Generating an XML File to Syndicate Posts to Aggregators

Here is what I'm trying to do:

Create a template which can take my posts (In this case "property") and serve an XML file so aggregators such as Zillow can syndicate my properties on their website.

I have reworked a plugin I found. It works, kind of, it only returns one result with an error. (See image:http://ift.tt/1wpSfal) when I have it set to the following:

    'posts_per_page'  => -1,

When I have it set to 1, it works perfect but obviously, I have more than 1 post.

    'posts_per_page'  => 1,

I'm a little baffled (Ok, really baffled) as to why this is happening. Below is the template.

 <?php
/**
 * XML feed generator template.
 */
header('Content-Type: ' . feed_content_type('rss-http') . '; charset=' . get_option('blog_charset'), true);
$more = 1;
echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>'; ?>
<?php
global $query_string;

$args = array(
    'numberposts'     => '',
    'posts_per_page'  => -1,
    'offset'          => 0,
    'cat'             =>  '',
    'orderby'         => 'date',
    'order'           => 'DESC',
    'include'         => '',
    'exclude'         => '',
    'meta_key'        => '',
    'meta_value'      => '',
    'post_type'       => 'property',
    'post_mime_type'  => '',
    'post_parent'     => '',
    'paged'           => '',
    'post_status'     => 'publish'
);

query_posts( $args );?>

<?php while( have_posts()) : the_post(); ?>

<Listings>
 <Listing>
  <Location>
   <StreetAddress></StreetAddress>
   <UnitNumber></UnitNumber>
   <City></City>
   <State></State>
   <Zip></Zip>
   <Lat></Lat>
   <Long></Long>
   <DisplayAddress><?php echo get_post_meta($post->ID, "nt_neighborhood", true);? </DisplayAddress>
  </Location>
  <ListingDetails>
  <Status></Status>
  <Price><?php listing_price();?></Price>
  <ListingUrl><?php the_permalink_rss() ?></ListingUrl>
  <MlsId><?php the_ID(); ?></MlsId>
  <MlsName></MlsName>
  <VirtualTourUrl></VirtualTourUrl>
  <ListingEmail><?php the_author_meta('user_email'); ?></ListingEmail>
  <AlwaysEmailAgent></AlwaysEmailAgent>
  </ListingDetails>
  <RentalDetails>
  <Availability><?php echo get_post_meta($post->ID, "nt_heating", true);?><   </Availability>
   <LeaseTerm></LeaseTerm>
   <DepositFees></DepositFees>
   <UtilitiesIncluded>
   <Water></Water>
   <Sewage></Sewage>
   <Garbage></Garbage>
   <Electricity></Electricity>
   <Gas></Gas>
  <Internet></Internet>
  <Cable></Cable>
  <SatTV></SatTV>
 </UtilitiesIncluded>
  <PetsAllowed>
 <NoPets><?php echo get_post_meta($post->ID, "nt_parking", true);?></NoPets>
  <Cats></Cats>
  <SmallDogs></SmallDogs>
  <LargeDogs></LargeDogs>
  </PetsAllowed>
 </RentalDetails>
 <BasicDetails>
 <PropertyType></PropertyType>
 <Title><?php the_title_rss() ?></Title>
 <Description><?php the_content(); ?></Description>
 <Bedrooms></Bedrooms>
 <Bathrooms></Bathrooms>
 <FullBathrooms></FullBathrooms>
 <HalfBathrooms></HalfBathrooms>
 <LivingArea></LivingArea>
 <LotSize></LotSize>
 <YearBuilt></YearBuilt>
 </BasicDetails>
 <Pictures>
 <Picture>
<PictureUrl></PictureUrl>
<Caption></Caption>
</Picture><Picture>
<PictureUrl></PictureUrl>
<Caption></Caption>
</Picture>
</Pictures>
<Agent>
<FirstName><?php the_author() ?></FirstName>
<LastName></LastName>
<EmailAddress><?php the_author_meta('user_email'); ?></EmailAddress>
<PictureUrl></PictureUrl>
<OfficeLineNumber></OfficeLineNumber>
<MobilePhoneLineNumber></MobilePhoneLineNumber>
<FaxLineNumber></FaxLineNumber>
</Agent>
<Office>
<BrokerageName></BrokerageName>
<BrokerPhone></BrokerPhone>
<StreetAddress></StreetAddress>
<UnitNumber></UnitNumber>
<City></City>
<State></State>
 <Zip></Zip>
</Office>
<OpenHouses>
</OpenHouses>
<Neighborhood>
 <Name></Name>
<Description></Description>
</Neighborhood>
<RichDetails>
<AdditionalFeatures></AdditionalFeatures>
<Appliances>
<Appliance></Appliance>
<Appliance></Appliance>
</Appliances>
<ArchitectureStyle></ArchitectureStyle>
<Attic></Attic>
<Basement></Basement>
<CableReady></CableReady>
 <CoolingSystems>
  <CoolingSystem></CoolingSystem>
</CoolingSystems>
<Deck></Deck>
 <DoublePaneWindows></DoublePaneWindows>
<ExteriorTypes>
<ExteriorType></ExteriorType>
<ExteriorType></ExteriorType>
</ExteriorTypes>
 <Fireplace></Fireplace>
 <FloorCoverings>
 <FloorCovering></FloorCovering>
 <FloorCovering></FloorCovering>
 <FloorCovering></FloorCovering>
</FloorCoverings>
<Garden></Garden>
<HeatingFuels>
<HeatingFuel></HeatingFuel>
</HeatingFuels>
<HeatingSystems>
<HeatingSystem></HeatingSystem>
</HeatingSystems>
<JettedBathTub></JettedBathTub>
<Lawn></Lawn>
<MotherInLaw></MotherInLaw>
<NumFloors></NumFloors>
<NumParkingSpaces></NumParkingSpaces>
<ParkingTypes>
<ParkingType></ParkingType>
<ParkingType></ParkingType>
</ParkingTypes>
<Patio></Patio>
<Porch></Porch>
<RoofTypes>
 <RoofType></RoofType>
</RoofTypes>
<RoomCount></RoomCount>
<Rooms>
 <Room></Room>
 <Room></Room>
 <Room></Room>
 <Room></Room>
 <Room></Room>
</Rooms>
<SecuritySystem></SecuritySystem>
<Skylight></Skylight>
<SprinklerSystem></SprinklerSystem>
<ViewTypes>
 <ViewType></ViewType>
 <ViewType></ViewType>
</ViewTypes>
<Waterfront></Waterfront>
<WhatOwnerLoves></WhatOwnerLoves>
<YearUpdated></YearUpdated>
<FitnessCenter></FitnessCenter>
<BasketballCourt></BasketballCourt>
<TennisCourt></TennisCourt>
<NearTransportation></NearTransportation>
<ControlledAccess></ControlledAccess>
<Over55ActiveCommunity></Over55ActiveCommunity>
<AssistedLivingCommunity></AssistedLivingCommunity>
<Storage></Storage>
<FencedYard></FencedYard>
<PropertyName></PropertyName>
<Furnished></Furnished>
<HighspeedInternet></HighspeedInternet>
<OnsiteLaundry></OnsiteLaundry>
<CableSatTV></CableSatTV>
<Taxes></Taxes>
</RichDetails>
</Listing>
</Listings>
  <?php endwhile;?>