Frustrating File Upload Error

I have a form that may or may not contain a file upload. When the user uploads a file the script works as it should. The problem is that when a user doesn't upload a file, I get an error that reads: "PHP Notice: No file uploaded in Unknown on line 0 PHP Warning: Cannot send session cache limiter - headers already sent in..." I have tried everything I can think of to keep it from erroring out...the sample logic is here: if($_FILES) { if(isset($_FILES['file_upload']) && $_FILES['file_upload']['name'] !="") { .. but the error still occurs. I have even went so far as to try to turn off the error reporting using: error_reporting(0); and that didn't work either. I am using PHP 4.2.1 under IIS Any ideas or suggestions? Thanks, Ron {