How do I retrieve a uri segment in a hook?

[eluser]Jelmer[/eluser]
I didn't mean it would have to be the define() statement, I used that as an example.

Bottom line still is that errors don't show unless they're fatal or possibly unless they happen after something. I can't tell from this, you'll have to find the mistake. You might try placing a exit() statement directly after fetching the URI - if you see the output: that's not what goes wrong, if you don't that might be what causes the error. But without the actual error you still don't know why.
Example:

Code:

// Change this
$x = load_class('URI')->segment(1);

// To this:
$x = load_class('URI')->segment(1);
exit ('segment 1: '.$x);