decrypt and concatenate strings in select

I want to do this:SELECT (CAST(DecryptByKey(LastName) AS NVARCHAR(200)) AS LastName + ', ' + CAST(DecryptByKey(FirstName) AS NVARCHAR(200)) AS FirstName) AS NameI've tried many variations of this but I usually get the error :The data types varbinary and varchar are incompatible in the add operator. or sometimes - Syntax error near AS.So how do you do this? (SQL Server 2014)Doug