Blank spaces in my Crosstab

I'm using Crystal 10. I have several summary fields in my crosstab. Three of those columns occasionally show blank spaces (depending on the date range I use), even though I've formated the cells to print a zero if there's no data. Even the borders disappear.

The only thing unique about these 3 columns is that they hold 'sums' rather than 'counts'. The zero formatting works for all other fields.

What can I do to stop this disappearing act. It makes the crosstab look really strange.If any one of the values in Null then Sum is Null
Make sure values are not null