Sounds like PHP tmp folder permissions are not set correctly so the image is unable to be moved/opened as needed. When a file uploads it's sent to PHP tmp. It's then moved, copied, opened & saved, etc.. from there. In the case of image fields the file is opened, processed, and saved to its destination. You should have this issue for all image uploads and maybe even file uploads. You'll need to contact your host or try using FTP to change the folders permissions.

Could be modsecurity rejecting it for whatever reason. Check server error logs to see if there's any further details. Be sure to test with debug mode and maximum error reporting enabled so further error information can be output.

This is normally caused by the PHP user not having write permission to tmp. The error is basically saying GD or ImageMagick (whichever you're using) is unable to open the _FILES that was just uploaded. So it can't open, process, then save it in its new destination like it needs to. Why this only affects 1 file doesn't make any sense unless modsecurity is stopping it or the file is corrupt and GD/ImageMagick is failing to open it due to corruption.