I have created a mov file in my album, which was uploaded via ftp batch and then later created a thumbnail for the movie and named it the same but with the .jpg extension on the end and FTP batch uploaded it as well to the same album. But it did not change the thumbnail of the movie? Did I miss something?
http://www.thephoenixmagazine.com/ThumbnailProblem.jpg
Post a deep link to the file - something like http://yoursite.tld/your_coppermine_folder/displayimage.php?pos=-XXX where XXX represents the file ID.