Seems like you should use FOR SELECT (can return multiple rows, often used
with SUSPEND) and not just SELECT (must return a single row when used in a SP).

Set

Create Procedure sp_Invoice_Labor

>(ServiceOrderId Integer)
>Returns
>(
>...
>)
>As
>Begin
> SELECT ...
> FROM LABORDETAIL A
> JOIN CLIENTEQUIPMENT B ON
>A.CLIENTEQUIPMENTID=B.CLIENTEQUIPMENTID
> WHERE A.SERVICEORDERID=:SERVICEORDERID
> Into ...;
> Suspend;
>End /* Procedure sp_Invoice_Labor */