Hi...
Check your internal table was declared with LIKE statement instead of TYPE.
I suggest you to use class:
DATA: fo_sdescr TYPE REF TO cl_abap_structdescr,
fs_component TYPE abap_compdescr.
DATA: your_line LIKE LINE OF "pv_tabname".
DATA: fs_fieldcatalogue TYPE slis_fieldcat_alv,
ft_fieldcatalogue TYPE slis_t_fieldcat_alv.
fo_sdescr ?= cl_abap_typedescr=>describe_by_data( your_line).
LOOP AT fo_sdescr->components INTO fs_component.
fs_fieldcatalogue-fieldname = fs_component-name.
fs_fieldcatalogue-ref_tabname = 'pv_tabname'.
APPEND fs_fieldcatalogue TO ft_fieldcatalogue.
ENDLOOP..
Hope to help
Bye