I have a number of identical sheets, and I'd like to be able to count
the occurances of a certain entry in a cell.

When I use the formula:

=COUNTIF('Sheet1:Sheet16'!H2, "W")

the cell displays ##### (error in value).

What's a formula I can use?

Also, I'd like to be able to do a similar thing, with non-blank values
(i.e. I'd like to count the number of non-blank cells across a number
of identical sheets).

Thanks in advance for your help.