XML Parsing Error: no element found

I'm running CKfinder 1.4.1.1 and on my local server it's running like a charm. No problems there.

I do get a problem when I install the same, working, CKfinder install to a different server.

Then, launching CKfinder (simply by loading ckfinder.html) gives me the following error:

URL requested: "http://{long_url_here}/_ckfinder/core/connector/php/connector.php?command=Init&langCode=en"

Server response:

Status: 500

Response text:

<?xml version="1.0" encoding="utf-8"?>

It looks like it doesn't get done making up an XML page, stopping right after the declaration. The empty XML file thus gives a parsing error: "XML Parsing Error: no element found".

PHP version on that server is the same as I'm running at home.
I've changed the $baseUrl and $baseDir accordingly, so that's not the problem. CKeditor, by the way, is running fine on that server, so it's only CKfinder that I'm having this problem with.

I have no idea what may be causing this. I see some people having similar problems with CKfinder's/(F)CKeditor's XML, but only in earlier versions, so if anyone else has run into this, I'd appreciate your comments.
What could be going on here?

Edit: I did some source-diving and it turns out it has something to do with CheckAuthentication() in Core/Config. I guess it's just having problems with the auth check, but somehow doesn't get to give the usual errors. Might figure this one out..