URL iView links to a blank page

Hi,

Can i get your inputs and possible fix to the issue below, I am quite new to Netweaver portal.

A user encounters a blank page when he clicks on a url iView in the portal.

I also noticed that there is a 'Certification Error' on the address bar of the portal.
A couple of users are experiencing the issue and they claim that they can access the link without problem before.

They cleared cache and tried different browser settings but still the same issue.

Thanks