Need help creating SSH key pair for Serv-U 12


I'm new to certificates so go easy please! I'm trying to setup SFTP/SSH on our Serv-U v12 FTP server. We have a digicert wildcard certificate which I used to setup the SSL connection but I'm stuck on setting up the SSH private and public keys. If I try to create a private key from "Server Limits & Settings" > "Encryption Settings" I receive an error: SSL Error: Can't create key file. If I try creating a key pair from a database user I receive the same error...

I'm lost and cannot find anything on the Google or Rhinosoft's website. Please help? I'm not sure if I can use the digicert wildcard cert for this or not.