Query Help (distinct Conflicts With Order By)

Seems easy but I can't get it to work

Table Services
Pk_Service
Service_Name
MyDate
Fk_License

Table Licenses
Pk_License
License_Name

I need to get all the services for one license, but only once, you'll see what I mean

Pk Service Service_Name MyDate Fk_Licence
1 Base 10/5/2004 5
2 Base 12/6/2004 5
3 Super Base 11/4/2004 5
4 Base 20/10/2004 5
5 Super Base 17/7/2004 5

there's about 7000 records with the same 4 services recurring all the time

All I want for one license is the all distinct services for a chosen date

If I select License 5, and today's date, 26/10/2004, I would need the latest service (closest date but has to be inferior or equal), in this case

Pk Service Service_Name MyDate Fk_Licence
4 Base 20/10/2004 5
5 Super Base 17/7/2004 5

Here's the query I have:

select distinct Service_Name from Services where Fk_License=5 where MyDate <= SelectDate order by DateDiff('d',SelectDate,MyDate) DESC

where Fk_License is to get only the services for a particular license
distinct if to only get each service once
MyDate <= SelectDate if to get only the services older than the selected date
order by is to get the latest service cause there will be a lot of services older than the selected date

they say distinct conflicts with order by

Anyone knows how to do this query right?