Hi I’m experiencing the same problem and been trying all tricks in this thread (of course including giving all folders and files in the upload folder 777 access).
My client is using a premium theme that comes with tons of custom made plugins. By deactivating Woo-Commerce and some of the theme related plugins I was finally able to upload images/files below 2mb!
Files above 2mb still gives the error message, the file will show up after page refresh but without thumbnail and preview. Even after deactivating ALL plugins this error remains.
