I would think this would work - but the SQL check says error near 
@toprows.
My non paramter query works fine.

CREATE PROCEDURE usp_processinfo
(
  @toprows  int=null
)
AS
IF  @toprows is not null or @toprows >0
Begin


SELECT TOP  @toprows [processinfo]   FROM [vaultProcess] 
where ( LEFT ([processinfo],2)=' u' OR ErrorMessage is not NULL)
order by [EntryDate] DESC,[ErrorMessage]
    
End

else
Begin

SELECT * FROM [vaultProcess] 
where ( LEFT ([processinfo],2)=' u' OR ErrorMessage is not NULL)
order by [EntryDate] DESC,[ErrorMessage]


End