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As a workaround have a look into setting up default images for posts…

https://www.studiograsshopper.ch/dynamic-content-gallery/documentation/
‘Docs – How to name and organise your default images’

This will at least replace the black error message you receive in the dynamic content gallery for each new post until there is a fix.

Same issue with our site.
After update to WordPress 3.5.2 the contents of the ‘Image URL’ field in the Dynamic Content Gallery Metabox doesn’t seem to save on post publish/update.
Have tested using full and partial URLs and doesn’t seem to save.

Just a quick update on this one, I found I was having issues with images not displaying in Firefox and IE but they were fine in Chrome. Seems to be the way Chrome dealt with the ampersands in the ‘thumbnail’ URLs.

Fixed this without changing any folder permissions, just replaced the following code in my /wp-content/plugins/shortcodes-ultimate/lib/images.php file.

from line 52…

$return[] = array(
	'id' => $attachment->ID,
	'image' => $attachment->guid,
	'thumbnail' => su_plugin_url() . '/lib/timthumb.php?src=' . $attachment->guid . '&w=' . $width . '&h=' . $height . '&zc=1&q=100',
	'link' => $linked,
	'name' => $attachment->post_title,
'description' => $attachment->post_content
);

…with the following…

$relativeurl = str_replace(get_bloginfo('url'), '', $attachment->guid);
$return[] = array(
	'id' => $image->ID,
	'image' => su_get_post_image( $image->ID ),
	'thumbnail' => su_plugin_url() . '/lib/timthumb.php?src=' . $relativeurl . '&w=' . $width . '&h=' . $height . '&zc=1&q=100',
	'link' => $linked,
	'name' => $image->post_title,
	'description' => $image->post_excerpt
);

…and similar changes from line 84, replacing the following…

$return[] = array(
	'id' => $image->ID,
	'image' => su_get_post_image( $image->ID ),
	'thumbnail' => su_plugin_url() . '/lib/timthumb.php?src=' . su_get_post_image( $image->ID ) . '&w=' . $width . '&h=' . $height . '&zc=1&q=100',
	'link' => $linked,
	'name' => $image->post_title,
	'description' => $image->post_excerpt
);

…with this…

$relativeurl = str_replace(get_bloginfo('url'), '', su_get_post_image( $image->ID ));
$return[] = array(
	'id' => $image->ID,
	'image' => su_get_post_image( $image->ID ),
	'thumbnail' => su_plugin_url() . '/lib/timthumb.php?src=' . $relativeurl . '&w=' . $width . '&h=' . $height . '&zc=1&q=100',
	'link' => $linked,
	'name' => $image->post_title,
	'description' => $image->post_excerpt
);

The ‘str_replace’ converts the absolute URL to a relative one and inside the ‘thumbnail’ array value uses regular ampersands (&) rather than the HTML code (amp;)