This error occurs when you run the puppet module subcommand on newly provisioned Windows nodes.
The Forge uses an SSL certificate signed by the GeoTrust Global CA certificate.
Newly provisioned Windows nodes might not have that CA in their root CA store yet.
Download the "GeoTrust Global CA" certificate from GeoTrust's list of root certificates and manually install it by running
certutil -addstore Root GeoTrust_Global_CA.pem.
Hope this Helps!