I switched to a new server yesterday and transferred all my files.
Now, I'm getting "Fatal error: Call to undefined function dirname() in" errors on just about any page.
The weird thing is it's only happening on one site, even though the same exact files/scripts are on other sites on the same server as well (different IP address, though).
What's also weird is that the problem is not a constant. A page will load, then a couple clicks later the same page will have the PHP error - even though absolutely nothing has changed.