Unable to connect to VPN with new smart card

[LewisK]

I use FortiClient VPN to connect to a server which belongs to the Department of Defense.  I was just issued a new Common Access Card (specialized smart card used by the DoD) and I can use it to access CAC-enabled web sites, but cannot connect to the VPN.  I get this message:

"Unable to logon to the server. Your user name or password or client certificate may not be properly configured for this connection. (-12)"

I have already cleared out all the existing certificates using IE so that the system would be forced to reload the certificates from the smart card.  I have no idea what else to try.  Thanks to anyone who can suggest troubleshooting steps.

I was originally using FortiClient 4 but upgraded to 5.4 in the hopes it would resolve the issue... it didn't.