This is NOT a problem with your theme but it took me a long while to figure that out as the symptom was displayed in your theme. I'll contact the plugin developer as well.
When I enabled this plugin, ALL the portfolio pages returned 404's. The portfolio page itself was intact but when you clicked on Read More you would get a 404. I had this plugin installed for a while before noting the 404's so it wasn't obvious there was a connection.
Even after I disabled this plugin, I continued to get 404 errors until I cleared the permalinks (by selecting a different, saving, and going back to my original permalink). So, again, difficult to identify.
For you and anyone who might have this problem and find this post, please check any plugins that do Custom Post Types and Custom Taxonomies FIRST and make sure you clear the permalinks at each step.
I'd love to have this fixed but I don't know if it is a theme issue or a plugin issue. I'll leave that to the respective developers to hash out.