Your CFFILE upload must be given a variable such as
FORM.myFile that is provided from the previous page. This is
provided as <INPUT TYPE="file" NAME="myFile" ... >. This, in
turn, let's the user browse to the file and select it for upload.
So under normal circumstances, the file that is passed th CFFILE
exists.
If the user browses to a file and selects it, then deletes
the file using Windows Explorer and then clicks "Submit", CFFILE
will throw an error, which can be caught using
CFTRY/CFCATCH.