If you've clicked cancel when the browser asks which certificate to use, it caches the answer and never asks again. If you're using Firefox, try going to Preferences -> Advanced -> Encryption and choose "Select one automatically" -- that usually fixes the problem.
If that's not the issue, please contact email@example.com if you need access to this webpage and include the following two lines:
SSL_CLIENT_S_DN_CN: ??? SSL_CLIENT_S_DN_Email: ???