Subquery returned more than 1 value - where clause

[jun333]

I have a query to deactivate some accounts that were activated. Basically it looks at the year_end_close table and any accounts that exist there are updated in the master table to an inactive status (A or B).\[code\]update master set account_type = case account_type when 'C' then 'A' when 'D' then 'B' else account_type endwhere account_num = (select account_num from year_end_close where account_type in('C', 'D'))`\[/code\]I get "Subquery returned more than 1 value" from the where clause - what am I doing wrong? When I comment out the where clause I no longer get that error, so it's something in that clause.