Yes..thats right guess.. same scenario I am facing..i have truncated table and then its allow me to drop..but my concern is its not allowing me to insert data.if you can please tell me why this is happening?

create table demo (id int primary key , name varchar2(500) not null)
insert into demo select level , initcap(dbms_random.string('A',5)) from dual connect by level < =50

create or replace procedure Insert_gtt(table_name varchar2)
is
sql_stmt varchar2(100);
create_table varchar2(200);
begin
create_table :='Create global temporary table ' ||table_name||' (ids Number, names varchar2(100)) ON COMMIT PRESERVE ROWS ';
execute immediate create_table;
sql_stmt := 'Insert into ' ||table_name|| ' select * from demo d where MOD(id,2) = 0';
execute immediate sql_stmt;
commit;
end;

declare
table_name varchar2(100);
begin
table_name := 'Table_'||to_char(systimestamp,'ddmmyyyyhh24missFF2');
dbms_output.put_line(table_name);
Insert_gtt(table_name);
end;

create unique index MyIndex on "Dynamically Generated Name" (IDS,NAMES);