calculating business hour including saturday error result

Hello, i have the formula to calculate between two dates but the result is uncorrect or error if i put the start/ time out of business hour.
Please help me and hope get solutions...
This is my formula

=(INT(I11)-INT(H11)-INT((WEEKDAY(H11-1)+INT(I11)-INT(H11))/7)-SUMPRODUCT((J2:J3>H11)*(J2:J3<I11)*(WEEKDAY(J2:J3)<>1)))*(I2-H2)+MOD(I11,1)-MOD(H11,1)

Explanation :
I11 = EndDate
H11 = StartDate
J2:J3 = HolidayList
I2 = EndTime
H2 = StartTime

Thx DLL for your respon, i've many read your solutions
Yes, sometimes i get End/StartDate out of business hour. Here i more explain my format so you can understand what i means...
all format :
End/StartDate = in different cell, mm/dd/yyyy hh:mm:ss
End/StartTime = in different cell, 07:30 --------> 20:00
HolidayList = mm/dd/yyyy
result = [h]:mm

So, for example data is 06/23/2013 21:00 in End/StartDate, i got the result become #######, formulas can't read time out of business hour...
meanwhile, if End/StartDate is in business hour, formulas is working
Expect you know the answer for me, thx a lot DLL

also if is in holiday,sunday