You receive one of the following errors in WordPress:
- The upload folder is not writable
- Unable to create directory
- Unable to create directory uploads/20xx/yy. Is its parent directory writable by the server?
In the WordPress admin panel, choose Settings > Media and erase the contents of the upload path to set it to default. If you wish to keep the option to set this, you can set the default manually: wp-content/uploads
Save settings, and this problem should be resolved.
If the problem continues, also check to be sure that your PHP configuration is set to FastCGI and not Apache Module in Plesk.
You receive an error like "The uploaded file exceeds the upload_max_filesize directive in php.ini" or "Input file not found" when uploading a file within WordPress
See Problem Resolution #2 below to solve this.
If you're uploading a large image or PDF within a reasonable limit like around 100MB or smaller, simply adjust your upload_max_filesize value within Plesk.
If that doesn't do the trick, you may need to adjust the post_max_filesize as well.
If you're uploading a larger file (> 100MB or so), even once these configuration values are changed it's difficult to say if a file of that size is going to upload fast enough before the standard web server process timeout is reached, at which point you'll run into an unchangeable limit.
If you're uploading a video file, you should know that most uploaded video files don't play across all devices; this is why most people upload the video to sites like Vimeo or YouTube, then embed the video on their site from there. Those services will convert the video to a variety of different formats and then load the one that plays best on whichever device is viewing the site/page. It is recommended to use one of those services for video uploads.
Otherwise, your best options is to upload the file using the Plesk file manager or FTP instead. Once in Plesk just choose "Files" and you'll find your website files under the httpdocs folder for your primary domain or whichever folder is showing in Plesk as the web root for add-on domains.