I checked your certificates for given users, I found that they were of different sizes. I changed the size and regenerated the certificate for the user and it worked fine.
Refer:
http://somup.com/cqXX1PfI6C
Note:
there are some key points you should understand.
when you regenerate a certificate, it doesn't save a certificate, it only regenerates the certificate.
for saving it you will have to click on certificate and wait to save the certificate. It may take some time.
Refer to a video here:
http://somup.com/cqXXiFfIXX
I had to wait for 20 sec in case of your site to update the certificate.