I'm experiencing something similar on my Joomla3 installation with Vihrea template.
By default the SEF URLs were enabled, and all the links for Portfolio items were broken due to incorrectness on the link itself:
wrong link : ../index.php/item/18-uis-arcu-tortor
correct link: ../index.php/
component/k2/item/18-uis-arcu-tortor
Disabling the SEF everything is ok.
I've tried to look around to understand where it comes from, but my knowledge on Joomla/PHP is not so strong...
Any clue?
Thanks in advance, and thanks as well for your rockin' templates

Daniele