Try:
=SUMPRODUCT(SUBTOTAL(3,OFFSET(B3:B5231,ROW(B3:B5231)-MIN(ROW(B3:B5231)),,1)),(B3:B5231>"19/7/2010"+0)*(B3:B5231<="15/8/2010"+0)*(P3:P5231="Powerpack")*(U3:U5231=1))
Note: range sizes must all be the same
A more universal approach to comparing date is to use the DATE() function... because the way your date is written wouldn't work in North America, for example.
=SUMPRODUCT(SUBTOTAL(3,OFFSET(B3:B5231,ROW(B3:B5231)-MIN(ROW(B3:B5231)),,1)),(B3:B5231>DATE(2010,7,19))*(B3:B5231<=DATE(2010,8,15))*(P3:P5231="Powerpack")*(U3:U5231=1))
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