That says that something in the thumbnails was corrupted, so the media scan never completed. You might also find a little better battery life now.
Just so you understand - if there's a ,nomedia file in /DCIM/Camera, nothing in /DCIM/Camera will be scanned, including any other folders in there, so no pictures of videos in there will be found, and Gallery only shows files that are found during a media scan, unlike the file manager that displays all files.
Also, .nomedia is a hidden file (because it starts with a dot), so searching for only non-hidden files won't find it..