getAttribute -> ERROR!

[masterpuppet]

Te sugiero que utilices DOMXPath, en tu caso podria ser asi:

Código PHP:

...
$doc = new DOMDocument('1.0', 'UTF-8');
$doc->loadHTML($html);
       
$xpath = new DOMXPath($doc);
 
foreach($xpath->query("//form[starts-with(@id, 'frmArticle')]//a") as $anchor){
    var_dump($anchor->getAttribute('href'));
}
 

o algo mas explicito.

Código PHP:

...
$doc = new DOMDocument('1.0', 'UTF-8');
$doc->loadHTML($html);
       
$xpath = new DOMXPath($doc);
 
foreach($xpath->query("//form[starts-with(@id, 'frmArticle')]/fieldset/div[@class='articleImages']/a") as $anchor){
   var_dump($anchor->getAttribute('href'));
}
 

Saludos.