“An SSL error has occurred and a secure connection to the server cannot be made.” 

This error was seen when browsing to HTTPS sites with Secure Web over a Full VPN tunnel. HTTP sites loaded correctly.

When traffic policies are in place to direct traffic to a proxy, two policies are required. One for HTTP and one for SSL (which uses the TCP protocol option)

Check your traffic is hitting the correct policy using "nsconmsg -d current -g _hits" from the Netscaler command line. You may need to tweak your policy evaluation to ensure traffic is hitting the correct traffic policy.