Never mind - managed to fix it. It was the flickrpress plugin used in the core plugins for the theme causing a fatal error. Once I removed this everything worked again,
Awesome - thank you.
So first mistake I realised is that I was wrapping multiple portfolio images in separate [portfolio] tags. i.e.
[portfolio][portimg]src="http://demo.csshover.pl/wp-content/uploads/2011/09/MonstersInc4.jpg"][/portimg][/portfoli…