First of all make sure your browser settings have not changed. Make sure that
only SSL 3.0 and TLS 1.0 are checked.
Have you recently changed/updated your CAC card? Not all cards are the same, some are Gemalto, some Oberthur, etc. Depending on which specific card you have, it's possible that you might have to update your ActiveClient software. Most cards don't need the ActivClient software in Windows 7, it works natively however some cards like the one I have (Oberthur 128 Dual 5.5) does need the .119 update in order to work, so in my case ActivClient is needed.
A great resource is through my friend Chief Danberry's site at
www.militarycac.com.
Make sure your CAC reader is detected by Windows (you can see it in the Device Manager), if not make sure it's enabled in VMWare.
Next is ensure that your CAC card's digital certificates are being downloaded onto your machine so that your browser can use them. You should have 3 certificates total. To manually pull them off your card, open up User Console (the cac card icon in the systray by right clicking it), then go to Tools > Advanced > Make Certificates Available to Windows. If all goes well you should see a pop up that shows your name and some certificates with some numbers.
Next re-download and install the latest DoD Certificates, found on MilitaryCac.com. If you can manually log into my.AF.mil, you can get them from there as well.
Next, clear your browser's cache and temp files, it may not be a bad idea to also clear the history in the process.
Still have issues? Check the AF section on Militarycac.com at the following link.
http://www.militarycac.com/airforce.htm