You need the alias of your subquery. However, you do not need to use a subquery for this. You can use SELECT DISTINCT directly. Also, avoid using old-style JOIN syntax and use an explicit JOIN expression instead.
However, if you want to use a subquery, your column must have unique names. Do this by adding unique aliases.
select * from( select distinct sar90.code as code1, sar90.state as state1, sar90.county as country1, sabet.code as code2, sabet.state as state2, sabet.county as country2 from [dbo].[sarshomari_90] as sar90 inner join [dbo].[Fixed] as sabet on sar90.county = sabet.county and sar90.state = sabet.state where sar90.state = N'kerman' )t
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