I have the same problem. Looks like the cause is Geeklog now requires Pear.
Make sure pear is installed on the server.
2 - require_once(HTTP/Request.php) [function.require-once]: failed to open stream: No such file or directory @ /home/www/system/classes/syndication/parserfactory.class.php line 31
// Require pear HTTP_REQUEST
My question, any workaround for the issue? (besides installing Pear) Or should I just migrate back to 1.5