Sumproduct. count how many time a month appears (in column filled by date or text). #Value

Hello everyone,

I hope my question has not been answered yet, I search for hours...
My column 'M' is filled by date (dd/mm/yyyy) but also by text ("hold").
basically, I want to know how many time a dedicated month (let's November, so month=11) appears in this column.

My formula is

Formula:

=SUMPRODUCT(--(ISNUMBER(M7:M75));--(MONTH(M7:M75)=11))

my column 'M' looks like this:

28/11/2012

Hold

28/11/2012

29/11/2012

29/11/2012

30/11/2012

1/12/2012

5/12/2012

6/12/2012

==> Without the "Hold", my formula indicate the result of "5" (november appears 5 times) so it is perfect.
==> With the "Hold", my formula gives "#value"

Any idea?