Default permitted_uri_chars msg not showing up, instead showing exception error msg

I have a project made using CodeIgniter v 3.1.10. In the Config.php i have the default setting:

Code:

$config['permitted_uri_chars'] = 'a-z 0-9~%.:_\-';

Now, when I manually modify the url for e.g. as xyz.com/cat/'. Please note the apostrophe at the end of the URL, then I'm expecting the default error message like -

Code:

An Error Was Encountered
The URI you submitted has disallowed characters.

But instead of the above error message I'm getting an uncaught exception error message

Can anyone please tell me what and where I need to change/Check. Thanks