In Codeignitor, its usual for the developer getting the Error: "Disallowed Key Characters"
This error used to drove newbies nuts. I am not sure about the reason and the fix provided by codeignitor help page not works some times[Most of the times from my experience]. It is also difficult to find what caused the error.
Here is solution that help in diagnosis of the problem.
In the core CI code in system/libraries is a file called input.php This small modification would show the actual data that caused the Problem.
Around line number 199
if ( ! preg_match(“/^[a-z0-9:_\/-]+$/i”, $str))
exit(‘Disallowed Key Characters: ‘.$str);
// The variable $str was added to display the data in question.