Upload file from my C drive to SAP

I have written a program where I upload a file using FTP to update info to SAP. This program works.

I now need to change this program NOT to use FTP, but to upload the file from my laptop's "C" drive (we need to not use FTP for various reasons). I have made changes to my program for this, but it gives a sy-subrc = 4 error where the bold sentence is.

    MOVE upload TO filename.
* Open the dataset
OPEN DATASET filename FOR input IN TEXT MODE.

IF sy-subrc = 8.
    WRITE: 'File - "', filename, '" , could not be opened.'.
    STOP.
ENDIF.
DO.

* Upload the contents of the file into internal table tbdata
    READ DATASET filename INTO itab.
   IF sy-subrc NE 0.
      EXIT.
    ENDIF.
    APPEND itab.
ENDDO.

* Close the Dataset
CLOSE DATASET filename.

Can anyone see where my problem is? It is a txt file on my TEMP file in my "C" drive. Any help will really be appreciated.

Regards

Debbie