I was also receiving this error message, with the following criteria confirmed: 1) add'l spaces in front of column headers/names were removed; 2) columns were all formatted to text; 3) file was in .txt format, or in .csv format (tried both).
The culprit was 1 field (column) contained 1,676 characters. I changed the column size to 250 or fewer (fixed position import) and it worked. Hope this helps.