If you are not able to upload a plugin or a theme to your Favorites extension and get the Could not save uploaded file, it is more than likely that the tmpfile() PHP function is disabled by your host.
- Go to the MainWP > Status > Server Information page
- Find the Disabled Functions check
- Verify that the tmpfile() PHP Function is disabled by your host
- If yes, contact your host support and have them enable it for you.