lennart5 on "Duplicate post type"

Hi everybody!
I'm working on a website that's using the WPZOOM Digital theme. On the front page of the website (www.bananagun.nl), a slider, a portfolio and a few blog items are displayed. My client wants to change this: the portfolio can stay as it is, but they want to have the blog items displayed in the slider.
I tried doing this by copying the 'Portfolio' custom post type and changing all instances of Portfolio to Slideshow (and portfolio to slideshow) and then telling the slider to look for slideshow posts instead of portfolio posts. However, as soon as I copy the custom post type (I tried pasting it in custom-post-types.php - where the Portfolio post type also is declared - and functions.php), I get the blank screen of death. Would anyone know how I can tackle this problem?
Thanks!!