I've installed to a subfolder /gallery

I've gone through the setup procedure ok, and the gallery appears to be working.

but i cant get into the addmin interface which is at:
http://www.noahwilson.co.uk/gallery/zp-core/admin.php

Fatal error: Call to undefined function rc4() in /home/nwilson/public_html/gallery/zp-core/functions.php on line 2449

any ideas what i did wrong?

You must be missing the file lib-encryption.php or it is corrupted.