file uploaded check

[eluser]pendalpusher[/eluser]
when i use this code

Code:

if ( $_FILE['userfile']['size'] > 0 )
{
    //the user has selected a file
}

i get the following error

Code:

A PHP Error was encountered

Severity: Notice

Message: Undefined variable: _FILE

Filename: controllers/banner.php

Line Number: 127

Any other suggestions would be great.
C