Native Database Query Error

I'm having this Expression.Error: This native database query isn't currently supported.

I declared some variables to update some dates in the Main Query.

Does anyone have an idea what's wrong here? It works fine when I run it in SQL Server.

DECLARE @Start_Date DATE, Anonymous_Date DATE, @Update_Date DATE, @Pay_Date DATE, @NextStart_Date DATE;

SELECT
@Start_Date =   dateadd(day, -1 * DATEPART(dy,SYSDATETIME()) % 14 , SYSDATETIME())
SET Anonymous_Date = dateadd(DAY , 13,@Start_Date)
SET @Pay_Date = dateadd(DAY , 19,@Start_Date)
SET @Update_Date = dateadd(day,-7, Anonymous_Date )
SET @NextStart_Date = dateadd(day,14, @Start_Date)


IF @Update_Date >= convert(date, SYSDATETIME() ) AND @NextStart_Date <= convert(date, SYSDATETIME()) 
BEGIN
<Main Query here>
END