smartforms problem

Hi experts,

Iam trying to display data through smartforms standard table.

In the global data i have declared t_det with refrenece to structure.

In the table Main area i have created one text and passing T_DET-LABST(It is MARD_LABST qty)field.

While executing the form it is through the error that

"Reference field T_DET-LABST unknown in form."

What might be the reason?

regards

sumit.