C_T_DATA field unknown error in DS Enhancement

Hi,

I Need to enhance an DS with two fields.

after enhancinh the fields i wrote the code in CMOD FUNCTION EXIT_SAPLRSAP_001.

I used the internal table C_T_DATA in the same.

But while checking the program i am getting the error the C_T_DATA is known.

As per my understanding this is an internal table and can be used for transactional data loading.

But i am getting the error teh field is unknown .Please suggest.