By bringing up their consoles, do you mean by clicking the button "Console "in the top right of the page?
If so, check Java as it is required to use this feature. You may need to manually add the servers address to Java Security Site list so that you can use it.
I made sure Java is installed correctly and everything on the machine I'm interacting with Proxmox on, and Java seems to load up fine, and yes, that's what I meant.
I'll go see if I can manually add it into Java's list.
Have you solved your problem yet? If you are using windows, you can use putty to SSH into the container. You would have to know the container's ip address.
When you are ssh'ed into the main server, have your tried entering "vzlist" without quotes at the command line? This lists the ip addresses for my containers.
Additionally if you connect to the main server through the web browser, you can double click a running container and the ip address should be under the "Network" tab for the container.