Server Administration :: ORA-39726 / Unsupported Add / Drop Column Operation On Compressed Tables

my user is trying to drop columns, but she gets below error:

SQL Error: ORA-39726: unsupported add/drop column operation on compressed tables

39726. 00000 - "unsupported add/drop column operation on compressed tables"

i just checked whether table is compressed or not, it is not compressed it seems:

select owner, table_name,COMPRESSION,COMPRESS_FOR from dba_tables
2 where owner = 'EQUIPMENT' AND TABLE_NAME = 'ETHRNT_VRTL_CNXN_HRLY_AGG_SWP';
OWNER TABLE_NAME COMPRESS COMPRESS_FOR
------------------------------ ------------------------------ -------- ------------
EQUIPMENT ETHRNT_VRTL_CNXN_HRLY_AGG_SWP DISABLED

1 row selected. i am able to set one column as UNUSED. and then i am able to see the count accordingly from below view:

select * from DBA_UNUSED_COL_TABS
where owner ='EQUIPMENT' and table_name = 'ETHRNT_VRTL_CNXN_HRLY_AGG_SWP';

but not able to drop the unused columns. if i tried to drop a column directly from the table, that also giving above error.