Ajax callback fails (but used to work)

[eluser]Ivoo[/eluser]
resolved!

It turns out that this problem (ajax callback results in 500 internal server error) can be caused by the

|--------------------------------------------------------------------------
| Cross Site Request Forgery
|--------------------------------------------------------------------------
| Enables a CSRF cookie token to be set.

The problem can be worked around by setting:

Code:

$config['csrf_protection'] = FALSE;

in CodeIgniter's /application/config/config.php file.

Don't ask me why, because I do not know. I just found an off-hand remark that pointed me in the right direction here.