a few things missing
1. FROM clause in the subquery
2. something that correlates the subquery to the table being updated, so only one row is returned
3. WHERE clause on the table being updated, so TurnTime values that don't fit the subquery aren't nulled [unless that's the desired behavior]

UPDATE TurnTimeTable
   SET TurnTime = (SELECT (DATECOMPLETE - DATESTART) as 'Turn Time'
   FROM TurnTimeTable t2 --< added FROM
   WHERE EmployeeID NOT LIKE '5%' AND EmployeeID NOT LIKE '9%'
   AND t2.PK = TurnTimeTable.PK --< correlate the subquery
)
WHERE EmployeeID NOT LIKE '5%' AND EmployeeID NOT LIKE '9%' --< update the correct rows

HTH


>Hi,
>
>I'm trying to update a column in a table like this.
>
>UPDATE TurnTimeTable
>SET TurnTime = (SELECT (DATECOMPLETE - DATESTART) as 'Turn Time'
>WHERE EmployeeID NOT LIKE '5%' AND EmployeeID NOT LIKE '9%'
>)
>
>
>Is there a way to do this without getting this error..
>

>Server: Msg 512, Level 16, State 1, Line 1
>Subquery returned more than 1 value.
>This is not permitted when the subquery follows =,
>!=, <, <= , >, >= or when the subquery is used as an expression.
>The statement has been terminated.
>