currently unable to handle this request. HTTP ERROR 500

Hello,

You would need to check your Plesk error log to see the actual error. To do so, you need to SSH to the server and then check the log at /var/log/sw-cp-server/error.log:

tail -100 /var/log/sw-cp-server/error.log

As described here a common cause of this problem is that you might have to set correct permissions to the following directories:

Set valid permissions for system directories:

chown root:root /tmp
chmod 1777 /tmp

chown root:apache /usr/sbin/suexec
chmod 4510 /usr/sbin/suexec

chown root:sw-cp-server /usr/lib64/sw-cp-server/sw-suexec
chmod 4710 /usr/lib64/sw-cp-server/sw-suexec

And finally restart sw-cp-server:

service sw-cp-server restart

Let me know how it goes. Regards, Bobby