Please Help

I have a code like this:

My purpose is to have a header in my excel summary report.

But there's an error like this:

"Field "gv_HEADING-TEXT" is unknown. It is neither in one of the

specified tables nor defined by a "DATA" statement. "DATA" statement."

sample code in my program:

data: gv_heading(10) type c.

gv_HEADING-TEXT = 'Company Code'.

append IT_HEADING.

gv_HEADING-TEXT = 'RFQ Number'.

append IT_HEADING.

gv_HEADING-TEXT = 'RFQ Line Item'.

append IT_HEADING.

call function 'GUI_DOWNLOAD'

exporting

FILENAME = L_FNAME

FILETYPE = 'DAT'

tables

DATA_TAB = IT_FINAL

FIELDNAMES = gv_HEADING

Please help me in solving this problem.

more points!!