Just an other "feature" of the rwd theme.
I assume you built your theme based on the rwd theme.
Make sure you have this in your catalog.xml
layout file of your theme inside the layout handle <PRODUCT_TYPE_configurable>
<reference name="product.info.options.wrapper">
<block type="catalog/product_view_type_configurable" name="product.info.options.configurable" as="options_configurable" before="-" template="catalog/product/view/type/options/configurable.phtml">
<block type="core/text_list" name="product.info.options.configurable.renderers" as="attr_renderers" />
<block type="core/text_list" name="product.info.options.configurable.after" as="after" />
</block>
</reference>
If that does not work , copy the file suggested in the error message to your theme and replace this:
foreach ($_renderers as $_rendererName):
$_renderer = $this->getChild('attr_renderers')->getChild($_rendererName);
if (method_exists($_renderer, 'shouldRender') && $_renderer->shouldRender($_product, $_attribute, $_jsonConfig)):
$_renderer->setProduct($_product);
$_renderer->setAttributeObj($_attribute);
echo $_renderer->toHtml();
$_rendered = true;
break;
endif;
endforeach;
with this:
$attRenderes = $this->getChild('attr_renderers');
if ($attRenderes) :
foreach ($_renderers as $_rendererName):
$_renderer = $this->getChild('attr_renderers')->getChild($_rendererName);
if (method_exists($_renderer, 'shouldRender') && $_renderer->shouldRender($_product, $_attribute, $_jsonConfig)):
$_renderer->setProduct($_product);
$_renderer->setAttributeObj($_attribute);
echo $_renderer->toHtml();
$_rendered = true;
break;
endif;
endforeach;
endif;