Nulls In Crosstab Query

I've been struggling with a problem and I hope one of you can please help.

I created a crosstab query that displays group names on the vertical axis and dates on the horizontal axis. I use a Count for the values. I use a pop-up dialog to get parameters for the dates (between... and), which are organized as Quarters. The query works fine and I can insert it into a report, which also works fine... with one problem. The dates only work when the date parameters request a year (4 quarters), and only work when each quarter has at least one entry. (Only work = I get an error message when one or both of these conditions are violated.)

Sometimes, I want to look at less than a full year, but when I use parameters for three or fewer quarters, I get an error. Same thing if I request a quarter that doesn't have any data. I assume the solution is to convert Nulls to Zeros and have wrestled with both Nz function and IIf, but have not been able to convert the values. I get the correct values in the quary's dataset if they are numbers, and blanks if no data, but no zeros anywhere. I also don't know how to make my report flexible or dynamic, so I can limit the number of quarters if I only want to look at a specific quarter or quarters (less than four).

Any ideas? Thank you so much for your time, and, Happy Holidays!

Stu