User have created a XD01 script with Internal number range. First transaction will run correctly, all other lines fail. The same issue can be applicable for transaction VD01.
Enable field RF02D-KUNNR in the mapper with a space for the upload value.
To enable the field, you'll want to open the mapper of your script. Open the Expert tab and click Filters in the top right corner. Uncheck the "Hide all disabled fields" option. Unchecking this option should reveal the RF02D-KUNNR field.
Check the checkbox in the Enable column for that row and a space in the Value column should automatically generate.
Save the script and attempt to run again and the field should clear for each Transaction.