You have to specify the size for your parameter otherwise it's char(1)

>VFP function used to call Stored Procedure:
>nSQLExec = SQLExec(nConn, "{Call RKR_GetShifts (cCalDate1)}")
>
>
>Stored Procedure:(SQLSVR 7.0)
>CREATE PROCEDURE [RKR_GetShifts]
>@SelectedDate as Char(11)
> AS
>Select tshiftstart, tshiftend
>From tblOESch_Shifts
>Where SubString(Cast(tshiftstart as char),1,11) = @SelectedDate
> Or SubString(Cast(tshiftend as char),1,11) = @SelectedDate
>Order By tshiftstart ASC
>
< SNIP >