I am having the same problem after upgrading from 2.1.3 to 2.4. I’m going to provide as much info from my troubleshooting that I can in hopes that it adds information to solve the issue.
My image files uploaded with safecracker do not show. Interestingly enough is that .zip files uploaded through safecracker in another file field do link and work fine. The database shows https://ellislab.com/asset/images/ent-partner-logo/media-image-fpo.jpg, but nothing outputs from the template tag. When I edit the content entry and try to upload a new image in place of the old I get an error stating “The upload path does not appear to be valid.” I get this same error when I try to upload images and .zip files in a new content item via safecracker.
The image files and the .zip fles upload to separate directories.
Prior to this error, I got an error immediately after upgrading that stated “Fatal error: Cannot redeclare class File_ft in /[removed]/system/expressionengine/fieldtypes/file/ft.file.php”. I deleted and replaced the /system/expressionengine/thirdparty/safecracker directory with the directory from the upgrade and the error went away. (this directory was originally copied during the upgrade but didn’t work until it was deleted and re-copied… go figure).
Looking for a solution…