Hi Eng,
Odds are good that the job scheduler just requires a restart. Generally, any time you see a 500 error, the best first step is to look for more information in the web server logs:
If it says anything about workers or jobs, then I would start by restarting the job scheduler and then repeating the import attempt. The following command should be run from AtoM's root installation directory - if you have followed our recommended installation instructions, this is generally /usr/share/nginx/atom.
On Ubuntu 14.04 with PHP 5.x:
On Ubuntu 16.04 with PHP 7.0:
- sudo systemctl restart atom-worker
Let us know if that helps. If not, please share any related information you find in the error logs.
Regards,