Please post your code. I'm nearly positive that you mistyped something.

Means the page can't find a function you are trying to use. The function called has to be in the page or in an included file to be used. That make sense??

If you could post the code that your running that's causing the error that would help.

However, It looks like your calling a function that doesn't exist.

It could have something to do with using register_shutdown_function() to call a function that is undefined.

"Note: Typically undefined functions cause fatal errors in PHP, but when the function called with register_shutdown_function() is undefined, an error of level E_WARNING is generated instead. Also, for reasons internal to PHP, this error will refer to Unknown() at line #0. "

Suggest checking your code for register_shutdown_function(). Hope that helps!