Sorry if this double-posts, but there seems to be problems today and I can't
see the post I thought I made.
The problem probably is that F2 or G2 contain spacebars, hidden characters,
or formulas that evaluate to "" or " ".
To clear up spacebars and hidden characters, select the cells and press Del.
To deal with the "" or " " change your formulas that read
='sheet2'!G2
to
=IF(sheet2!G2="",0,sheet2!G2)
If there is any other text in G2 then you might do
=IF(istext(sheet2!G2),0,sheet2!G2)
this second solution will work for the "" problem also.
cheers,
Shane