Symfony 1.2: Error when adding/editing entry in admin module

Question

I get this error when trying to run the model module "user" in the app "backend" with backend_dev.php/user, then clicking "New" and adding some data:

Warning: array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in C:\xampp\htdocs\sf_sandbox\lib\symfony\util\sfParameterHolde r.class.php on line 53

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\sf_sandbox\lib\symfony\util\sfParameterHolde r.class.php:53) in C:\xampp\htdocs\sf_sandbox\lib\symfony\response\sfWebRespons e.class.php on line 335

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\sf_sandbox\lib\symfony\util\sfParameterHolde r.class.php:53) in C:\xampp\htdocs\sf_sandbox\lib\symfony\response\sfWebRespons e.class.php on line 349

Also, the fields that I filled in are returned with *Required tags, indicating that they weren't submitted somehow. Even the CSRF token is missing according to the response from the form.

I followed the "Admin generator" tutorial, so I'm not sure what went wrong.

Thanks for any help!