Failed to save SSL options

Failed to save SSL options : The SSL private key file /etc/webmin/miniserv.pem does not exist or does not contain a PEM format key

Everytime I try to save SSL options in webmin (Webmin tab -> Webmin Configuration -> SSL Encryption -> Save) it spits out the above error. I've tried with a fresh operating system install three times, Self signed certificates, and the default webmin certificate, lets encrypt certificates. No matter what PEM i point it to, it complains its not correct format. EVEN with the default certificate webmin itself creates on initial install.

Operating system: Debian Linux 9 Webmin version: 1.860 Usermin version: 1.720 Virtualmin version: 6.01