I'm applying the conditional format =ISERROR($A$1) to change the text of
cells displaying #N/A to white, as recommended by every conditional
formatting guide on the Internet. However, when applied to a range of cells,
they all turn white!!

Cell A1 has a formula that provides a #N/A error, in the same way that the
desired cells produce an #N/A error:

The cells that need to be white are coded =VLOOKUP(B4,SHEET1,10) where B4 is
='SHEET2'!C4. C4 is blank, so B4 returns 0. The result is #N/A. (When C4 is
no longer blank, B4 displays data and needs to be visible.)

This is the only conditional format used in the spreadsheet. I've tried to
find out if anyone else has this problem and had no luck.