FlickrShow WordPress Plugin.
This is a common error message recieved due to the image_size option not set correctly. To verify the largest available image size for the images being fetched from flickr open an image on flickr.com by clicking the image. The image will load into the flickr.com fullscreen image veiwer. In the upper right hand corner of the window there is a button labeled "view all sizes". Click this button to verify that the image has the "Large" size available. If the Large size is not listed then find the largest size listed in the "view all sizes" list and add the image_size="largest size available" into your shortcode. example for an image that has the largest available size of medium 500: [flickrshow set_number="2178671637816" image_size="Medium 500" ]
You can easily obtain a flickr api key by going to the following link: http://www.flickr.com/services/apps/create/apply