Default controller not working

[eluser]wallern[/eluser]
Hi, I just pulled out an old version of CI (1.7.2) website from ftp, doing some upgrade work. However, after configuration in config, routes, database, .htaccess, I cannot get my default controller running. It looks like the default controller is called but cannot be executed. When I echo out something above the default controller, it appears. Other than that I get a blank white page.

As I'm not quite familiar with older version of CI, appreciate if anyone could give me some advise, maybe I missed something. Thanks in advance!