It's  all good I cracked  the joins, just had to repeat the joins twice as such...

WITH Base AS (
SELECT
  CSM.[First name]
 ,PP.[Fname]
 ,CSM.[Last name]
 ,PP.[Lname]
 ,[l].[ProfileId]
  , [l].[Date]
  , [l].[Paid]
  , [rn] = ROW_NUMBER() OVER (PARTITION BY [l].[ProfileId] ORDER BY [l].[Date] DESC)
FROM
  [dbo].[Ledger] AS [l]
 Inner Join personalprofiles PP
ON
L.ProfileId = PP.ID
Inner Join CurrentStudentMembership As CSM
on
CSM.[First name] = PP.[Fname]
And CSM.[Last name] = PP.[Lname]
Where [l].[Paid] > 0
)
SELECT
 CSM.[First name]
 ,PP.[Fname]
 ,CSM.[Last name]
 ,PP.[Lname]
,  .[ProfileId]
  , .[Date]
  , .[Paid]
FROM
  [base] AS
 Inner Join  Ledger L
 on .[ProfileId] = L.[ProfileId]
  Inner Join personalprofiles PP
 ON
L.ProfileId = PP.ID
Inner Join CurrentStudentMembership As CSM
on
CSM.[First name] = PP.[Fname]
And CSM.[Last name] = PP.[Lname]
Where [l].[Paid] > 0
and .[rn] = 1;