Cisco AAA/Identity/Nac :: Getting Certificate Installed - ACS 5.2

Currently I'm using a self signed cert issued by ACS. We are having an issue where occasionally we see in our Windows 7 logs that Windows did not like the self signed cert from ACS when doing dot1x authentication for our Windows 7 clients. We are using the built in dot1x client that comes with Windows and have the "Validate Server Certificate" unchecked but still see this error occasionally. I've tried issuing a CSR from the ACS server and going to Thwate and getting a test cert but everytime I paste the CSR into the field at Thwate I get an error about invalid cert type. You have to choose from a list of server types. I've tried several different ones. I've also tried issuing the request from a WIndows server and when I try and import the files I get a invalid key error. How to get certificate working from Thwate or Verisign?