SQL Query runs on SQL Server, but not on SQL Server Compact

Hello together,

this query works fine on MS SQL Server, but not on SQL CE:

select a.Gender
, a.Last_name
, a.first_name
, b. level
from patients  a left outer join (select x.id
, x.PatID
, x. level
from level x
where x.id = (select max(x1.id)
                       from level  x1
                       where x1.PatID  = x.PatID )) b
on (a.PatientID  = b.PatID )

Please help me, how to resolve it to work on SQL Server Compact!

Thanks

Mario