Data Source enhancement with ABAP....

My requirement is to enhance Z data source to include

bonus_cat,perfinc and active from ztrm_labdlycat table.

For that reason i appended the extract structure and in CMOD included the following code in EXIT_SAPLRSAP_001 as this is transaction data source

<b>CODE:</b>

case i_datasource.

when ' Z_TRM_LMS'.

Loop at case i_datasource.

when ' Z_TRM_LMS'.

Loop at i_t_data.

Select single bonus_cat perfinc active from ztrm_labdlycat into

i_t_data-zzbonus i_t_data-zzperf i_t_data-zzactive

Where locat = i_t_data-locat and

exrsn = i_t_data-exrsn and

apobj = i_t_data-apobj.

Modify i_t_data.

Endloop.

Endcase.

<b>ERROR</b>

The field "I_T_DATA" is unknown, but there is a field with the similar name "C_T_DATA".

I am new to BW and not familiar with ABAP code...please update me on this how can i correct error

Thanks