Invalid ColumnName frDate

Hi

I have below code

Declare @frDate as Datetime
Declare @toDate as Datetime


set @frDate = (select min(ta.TaxDate) from OWTR ta where ta.TaxDate >= '[%0]')
set @frDate = (select min(ta.TaxDate) from OWTR ta where ta.TaxDate <= '[%1]')

Select T0.DocNum,T0.TaxDate,T1.ItemCode
from Owtr T0 inner join Wtr1 T1 on T0.DocEntry = T1.Docentry
Where T0.TaxDate between @frDate and @toDate

Thanks