Intersect and order by

Hi,

I don't understand what's happening with my command
I read postgresql docs, it should work...What's the problem ?
The command is :

select col1
from table
where <conditions 1>
intersect
select col1
from table
where <conditions 2>
order by col1

It does not work and return "get_sortgroupclause_expr: ORDER/GROUP BY
expression not found in targetlist"

I use pgsql 7.03 ont redhat 7.0.

Any help would be appreciated

michael