I'm also experiencing this error. It's been really frustrating trying to pin down what the problem is.
Here's a little more detail on the error...
It only appears when you first load the DokuWiki. A refresh makes it go away, and the page displays normally. The title of the page isn't "start" like you would expect, its "array." Once you refresh, the error doesn't come back, unless you close the browser window and navigate back to the page.
I first started experiencing this with Radek's modified version from http://blogcms.com/
In order to fix the problem, I tried installing a fresh, unmodified copy from the DokuWiki site (dokuwiki-2005-05-07) and experienced the error as soon as I created the "start" page.
I've rechecked the file and Apache permissions several times now. Could this be a PHP setting issue? I'm on a hosted site, so I can't be certain northing's changed. A quick resolution will ease my headaches.