On the web, it’s standard practice to have your logo a clickable link which takes the visitor to your home page. Although I have seen the occasional business website which doesn’t allow you to click on the logo, I haven’t seen any that break the website when the logo is clickable.
Until now.
It seems that the people behind Sensis, the “search engine for Australians”, could have used a little help with their acceptance testing before they went live:

It appears that the Sensis programmers have made the assumption that a visitor will always enter their website via the home page, where a “session identifier” is established, presumably to track what the visitor is doing. If the visitor tries to access some of their pages directly, their application successfully detects that the “session identifier” isn’t set and attempts to set it by including it as a URI parameter for every internal link, including the home page.
And that’s the problem, right there.