how to fix this error?

[eluser]patrickpopowicz[/eluser]
When I build a quick form and validation for the sig_key, I'm not running into any problems. Everything submits, and validates okay including trim, xss_clean, required and the callback function.

There is something else causing the error. After looking at the code again, you are using non-validated variables to make your calls to the databases. You are setting them ($username, $password, and $sig_key) before you even validate the data, you should be setting those AFTER you validate okay.

In your original code, where are you setting the sig_key to the session? If you aren't setting it at all the callback will fail.