How do I enable CI error log

[eluser]WanWizard[/eluser]
In the category "stupid questions":

Why make it to difficult? Why not store this file in the helpers directory (where it should be), and simply use $this->load->helper()?

If you work cross-platform you have to be extremely careful with path manipulations like this. Paths on Windows use a backslash, not a forward slash. Sometimes, PHP converts them on the fly, sometimes not. And hardcoding a '/' is hardly ever a good idea.
If you insist, use the constant DIRECTORY_SEPARATOR instead of hardcoding the slash.