Are there any non printing characters in the apparantly blank cells. For
instance if you insert the following formula in a cell then it does not
display anything but you can see the formula in the formula bar:-

=""

If you then select the cell and Copy-> Paste Special-> Values over top of
itself, you will not see anything in the cell or the formula bar but if you
use the Ctrl + Arrow, it will stop on the cell because there is something in
it.

What I usually do with these is insert a new column A to the left of my data
and create a master index by inserting the following formula:-

= ROW() and copy it down to the full length of the data.

Then select the entire column and Copy->Paste Special->values over top of
itself to remove the formulas. (Don't forget to do this step)

I then sort on the columns with the non displayable data and can usually
then select these cells as a group and delete the data. I then resort on the
A column which is effectively the original index.

If OssiMac's guess is correct about converting ="" to values, then this is how I
clean them up:

Saved from a previous post:

If you want to see what's left in that cell after you convert ="" to values,
try:
Tools|Options|Transition Tab|Toggle Transition Navigation keys on.

Then select one of those cells and look at the formula bar.  You'll see an
apostrophe.  (Don't forget to toggle the setting to off.)

When I want to clean up this detritus, I do this:

Select the range (ctrl-a a few times to select all the cells)
Edit|Replace
what:  (leave blank)
with:  $$$$$
replace all

Immediately followed by:
Edit|Replace
what:  $$$$$
with:  (leave blank)
replace all