What was your process for generating the client certs?
If your easy-rsa batch files are new and unmodified, you should be able to do all of these steps with no errors:
Start->run->cmd
cd C:\Program Files (x86)\OpenVPN\easy-rsa
vars
clean-all
build-ca
build-key-server server
build-key client1
build-key client2
build-key client3
[EDIT] Cancel what I just said. I updated my OpenVPN and now having major issues with easy-rsa. It seems very broken right now.
The conversation is continued here:
https://forums.openvpn.net/post13785.html