[eluser]barbazul[/eluser]
There isn't much we can tell you about this error if you don't post more info.
Line 146 looks like this:
Code:
if ($this->CI->validation->valid_base64($string) === FALSE)
So either $this->CI or $this->CI->validation are not set.
Considering that line 144 looks like this:
Code:
$this->CI->load->library('validation');
and doesn't raise an error I'd say that there is something wrong with your loading class.
This are just wild guesses. Please provide with some examples of your controller code and what version of PHP and CI you're running