What could be the reason for this error? This is on a customer site.
Initially I was able to access the Portal.
I browsed to https web version of an AS in chrome and installed the certificate, the portal is showing Access Denied error.
I deleted the certificates, but still see the same issue.
The processors are running in the background but I am unable to get to the portal.
Accessibility to the portal has nothing at all to do with an AS. It does however have everything to do with how the portal is configured. Your screen shot indicates that the portal is configured on the loopback address. So you'll only have access to it if you are physically on that box or RDP'ed into it. Where exactly did you install a certificate? If it's on the SmartConnector box, you'll need to change the address of the portal to use that.
The SmartConnector service is on the same machine where I am using 127.0.0.1.
I installed the following certificate on the same machine. But I deleted them later assuming that they might have caused the issue.
Is there something I need to check on proxy settings or IIS or any certificate to install?
SmartConnector doesn't use IIS.
Please review section 12 of the SmartConnector Installation and Configuration Guide.pdf for how to configure SmartConnector with certificates.