Can't save new nginx virtual host - "virtualmin-nginx/save_server.cgi 500 (Perl execution failed)"

When creating a new nginx virtual host (https://:10000/virtualmin-nginx/edit_server.cgi?new=1&xnavigation=1) and clicking 'Create', the spinner spins and nothing happens.

Inspecting the console I see an error:

"https://:10000/virtualmin-nginx/save_server.cgi 500 (Perl execution failed)"

System details:

Webmin version: 1.900 Usermin version: 1.751 Virtualmin version: 6.05 Kernel and CPU: Linux 4.4.0-141-generic on i686 Processor information: Intel(R) Xeon(R) CPU E5-2650L v3 @ 1.80GHz, 1 cores