thumbnails of plugin suddenyl disappeared in dashboard and website

Hi there,

all of the thumbnails of plugins suddenly turn to grey including the theme’s thumbnail and fail to show in both dashboard and website, just like the flag of Qtranslate which fail to display when activating the plugin anymore

I have no idea of why it would happen, i just added the code last night to wp-config.php: define(‘WP_MEMORY_LIMIT’, ’96M’);