Please use Internet Explorer for this site
I tried internet Explore (ver 11) but I got the same error. What you can do do is downgrade your IE. Hit F12 to go into F12 debugger mode, there select the last TAB “Emulation”. Go to “User Agent” and select “Internet Explorer 8”. At this point reload you should be able to see the login page which was other wised replaced by the message above.
But you might still get lots of other error esp from debugger. I was help out by SECP staff to try the following (I have not tried it yet myself).
1. To Internet Explorer (IE) > Options and add www.secp.gov.pk to trusted sites (he actually mentioned to add to to compatible sites).
2. To got IE > Options > Security TAB. Select Custom and enable all checkboxes.
Will have to try this myself but it is here if anyone else has problem with SECP website.