Urgent---what is wrong

<b>Data: begin of itab occurs 0,

coursenum like zcourses-coursenum,

courseType like zcourses-coursetype,

location like zofferings-location,

instructor like zofferings-instructor,

duration like zcourses-duration,

end of itab.</b>

<i>data: l_fieldcat TYPE SLIS_T_FIELDCAT_ALV.</i>

data: repid like sy-repid.

CALL FUNCTION 'REUSE_ALV_FIELDCATALOG_MERGE'

EXPORTING

I_PROGRAM_NAME = repid

I_INTERNAL_TABNAME = 'itab'

I_INCLNAME = repid

CHANGING

CT_FIELDCAT = L_FIELDCAT

EXCEPTIONS

OTHERS = 3.

I could not get the field catalog from this internal table.

What is the problem?

Thanks.