GUI_UPLOAD: cannot interpret data in file

Dear Experts,

Im trying to upload simple CSV file into ALV and I'm getting the error message from GUI_UPLOAD: cannot interpret data in file.

What could be wrong at this:

DATA: ta_csv_data_raw  TYPE STANDARD TABLE OF zst_preisupload,

         wa_csv_data_raw  LIKE LINE OF ta_csv_data_raw.

zst_preisupload:

GUI_UPLOAD:

  v_filename = p_fname.

   CALL FUNCTION 'GUI_UPLOAD'

     EXPORTING

       filename = v_filename

       filetype = 'ASC'

     TABLES

       data_tab = ta_csv_data_raw.

Thank you!