When configuring a Windows Ops Manager for SSL, the conf-mms.properties file needs to include:

mongodb.ssl.CAFile=<path to CA File>
mongodb.ssl.PEMKeyFile=<path to PEM Key File>
mongodb.ssl.PEMKeyFilePassword=<password>

The paths would be expected to be written as:
D:\Certificates\cert.pem

This throws an error shown in the attached file.

They need to be written as:

D:\\Certificates\\cert.pem

to work properly.