I need to count the number of rows in which:

1. The date in column B falls within October 2007
2. Column G contains "MK"
3. Column O contains "SD"
4. Column Q contains "Stage"

I've tried this formula:
=SUMPRODUCT(--(TEXT('[Combined ESQ Notes.xls]Combined
Notes'!$B:$B,"yyyymm")="200710")*('[Combined ESQ Notes.xls]Combined
Notes'!$G:$G="MK")*('[Combined ESQ Notes.xls]Combined
Notes'!$O:$O="SD")*('[Combined ESQ Notes.xls]Combined Notes'!$Q:$Q="Show"))

....and it gives me a #NUM! error. Can anyone tell me why, or suggest a
correction?

Thanks in advance for any help you can give me!