I have just started to look into the decommissioning of a VMware vSphere 5.0 environment for a client as they prepare to upgrade to vSphere 6.0. When I tried to log into the webclient I was faced with this screen on Chrome V45 and similar in IE11:
After a bit of research and a good pointer from @sammcgeown I found that if I use an older browser (I tested a few but settled on Firefox 37.0.1), the error message went away and was replaced by a new issue:
As there is no solution to the issue as outlined in the KB article, but I found that if you set your clock back (I changed it to Jan-2015), the issue is resolved.
There are some blog posts on how to fix the certificates but for a quick and dirty solution I hope you find this helpful!