SQL*Loader Error Message

I am trying to load data from a flat file into an Oracle table and getting an error message of Field in data file exceeds maximum length for values in a column that exceed 256 characters. The field size on my source database, which I am creating theflat file from, is a VARCHAR2(500) and in my temp table, which I am trying to load the data into when I’m getting this error message, has a VARCHAR2(1000) field size. I’m not understanding why this is happening. Can anybody help me?