For kicks, I also increased the following items in php.ini
max_execution_time now at 3000 seconds
post_max_size now at 100M
upload_max_filesize at 100M
I've also rebooted the server incase there was some service that needed restarting.
The "cannot access" error comes up within a second of pressing the "Ok, submit" button so I don't think there's a timeout happening.
I'm running 6.4.1 if that matters.