error on the first page

Your filenames in the error message still aren't correct (they should be Mpages.php and Cpages.php, rather than mpages.php and cpages.php).

A quick search on this error message indicates that it usually shows up when using HMVC or some test frameworks, though it might also show up when calling a controller from a controller without either of those in place (because you shouldn't call a controller from a controller).

In any case, you're not including enough code to track down the problem (you haven't even included the code that loads the form validation library), and your error messages still show other problems (which may not be related to this specific problem, but will probably cause other problems once you do get everything else working).

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide