CodeIgniter fans might want to take note of this tip from Tiffany Brown concerning "disallowed key character" error messages.

After 6 hours of massive anxiety, stress, near tears, one pound on my desk, and some hair pulling, I tracked down the source of a nagging Disallowed Key Character error that I received while using CodeIgniter: an extra line break.

She eventually figured out that the newline and carriage return characters are not allowed as a part of the framework. Unfortunately, it was a random newline after a controller's code that did it for her.