Hi Piritia See,
Do you mean that you are attempting to add optional fields to your DirectRT input file. If so, then are you naming your columns with ! as the first character of the name? I would also suggest that you use only alphanumeric characters and no spaces in your column names.
Please feel free to upload an example of your DirectRT input file and I will be happy to take a look at it.
Cheers.
Jason