Tried To Execute A Query That Does Not Include The Specified Expression 'LastName' As

This is the SQL from a query for a Payroll report. It was an already existing report, so I'm trying to modify it to meet the business's needs. The problem is that there are multiple entries for WOLabor.Hours for a given day. These entries come from the invoicing program when a mechanic's hours are logged for billable time. So there may be 3 hours here and 1.5 hours there...but all for the same day. Payroll is just concerned with total hours worked...so I'm trying to combine all the hours for a given day into one variable or something and use that. I know this is long, but apparently a lot of fields are involved:

THIS GIVES ME NO ERRORS:

Code: Original - Code SELECT Person.LastName, WOLabor.MechanicNo, WOLabor.WONo, WOLabor.Hours, WOLabor.MechanicName, WOLabor.DateOfLabor, WOLabor.LaborRateType, WOLabor.SaleDept, WOLabor.SaleCode, IIf(WoLabor!laborratetype="R",IIf(wolabor!salecode<"P",[Hours],0)) AS Regular, IIf([regular] Is Null,0,[regular]) AS Reg, IIf(WoLabor!laborratetype="P",[Hours],0) AS [Double], IIf(WoLabor!laborratetype="O",[hours],0) AS Overtime, IIf(wolabor!salecode="R",[Hours],0) AS Holiday, IIf(wolabor!salecode="V",[Hours],0) AS LT, IIf(wolabor!salecode="U",[Hours],0) AS npay, IIf(wolabor!salecode="T",[Hours],0) AS Sick, IIf(wolabor!salecode="P",[Hours],0) AS Meet, IIf(wolabor!salecode="S",[Hours],0) AS vac, IIf([Hours]<=8,[Hours],8) AS PayrollReg, IIf([Hours]>8,[Hours]-8,0) AS PayrollOT, SaleCodes.LaborDescription, WOLabor.Cost, WOLabor.Sell, Person.Branch, Branch.Name, Dept.TitleFROM (((WOLabor INNER JOIN SaleCodes ON (WOLabor.SaleBranch=SaleCodes.Branch) AND (WOLabor.SaleDept=SaleCodes.Dept) AND (WOLabor.SaleCode=SaleCodes.Code)) LEFT JOIN Person ON WOLabor.MechanicNo=Person.Number) INNER JOIN Branch ON SaleCodes.Branch=Branch.Number) INNER JOIN Dept ON (SaleCodes.Dept=Dept.Dept) AND (SaleCodes.Branch=Dept.Branch)WHERE (((WOLabor.DateOfLabor)>=[Start Date] And (WOLabor.DateOfLabor)<DateAdd("d",1,[End Date])) AND ((Person.Branch) Like IIf([Enter the Branch Number or "All" for all:] Like "A*","*",[Enter the Branch Number or "All" for all:])) AND ((WOLabor.Transfer)=False))ORDER BY WOLabor.SaleDept, WOLabor.SaleCode; SELECT Person.LastName, WOLabor.MechanicNo, WOLabor.WONo, WOLabor.Hours, WOLabor.MechanicName, WOLabor.DateOfLabor, WOLabor.LaborRateType, WOLabor.SaleDept, WOLabor.SaleCode, IIf(WoLabor!laborratetype="R",IIf(wolabor!salecode<"P",[Hours],0)) AS Regular, IIf([regular] Is Null,0,[regular]) AS Reg, IIf(WoLabor!laborratetype="P",[Hours],0) AS [Double], IIf(WoLabor!laborratetype="O",[hours],0) AS Overtime, IIf(wolabor!salecode="R",[Hours],0) AS Holiday, IIf(wolabor!salecode="V",[Hours],0) AS LT, IIf(wolabor!salecode="U",[Hours],0) AS npay, IIf(wolabor!salecode="T",[Hours],0) AS Sick, IIf(wolabor!salecode="P",[Hours],0) AS Meet, IIf(wolabor!salecode="S",[Hours],0) AS vac, IIf([Hours]<=8,[Hours],8) AS PayrollReg, IIf([Hours]>8,[Hours]-8,0) AS PayrollOT, SaleCodes.LaborDescription, WOLabor.Cost, WOLabor.Sell, Person.Branch, Branch.Name, Dept.TitleFROM (((WOLabor INNER JOIN SaleCodes ON (WOLabor.SaleBranch=SaleCodes.Branch) AND (WOLabor.SaleDept=SaleCodes.Dept) AND (WOLabor.SaleCode=SaleCodes.Code)) LEFT JOIN Person ON WOLabor.MechanicNo=Person.Number) INNER JOIN Branch ON SaleCodes.Branch=Branch.Number) INNER JOIN Dept ON (SaleCodes.Dept=Dept.Dept) AND (SaleCodes.Branch=Dept.Branch)WHERE (((WOLabor.DateOfLabor)>=[Start Date] And (WOLabor.DateOfLabor)<DateAdd("d",1,[End Date])) AND ((Person.Branch) Like IIf([Enter the Branch Number or "All" for all:] Like "A*","*",[Enter the Branch Number or "All" for all:])) AND ((WOLabor.Transfer)=False))ORDER BY WOLabor.SaleDept, WOLabor.SaleCode;
When I make the following changes to the SELECT section, I get this error:

You tried to execute a query that does not include the specified expression 'LastName' as part of an aggregate function.

Code: Original - Code ... IIf(Sum([Hours])<=8,Sum([Hours]),8) AS PayrollReg, IIf(Sum([Hours])>8,Sum([Hours])-8,0) AS PayrollOT, ... ... IIf(Sum([Hours])<=8,Sum([Hours]),8) AS PayrollReg, IIf(Sum([Hours])>8,Sum([Hours])-8,0) AS PayrollOT, ...
Any insight is greatly appreciated.