Because the Wizard, in its wisdom thinks that what you should have and
hasn't spotted your SortingGrouping possibilities.

Ignore it. You can set up far better grouping and Sorting Levels using the
Sorting/Grouping box in Report Design View.
You can also make your own subforms and subreports quite easily without
having to wake up the Wizard at all, just by using the Link Master/Child
fields in the subreport/form's Properties.

In Acc97 using Sorting/Grouping with the wizard often made the report hang
so I've got used to doing without it.
Ironically, with Acc2000 I am frequently forced to re-instate the wizard
because I get sometimes Subscript out of range when I try to use
Autoreports - (I guess it's getting its revenge!)

Having said that however, yes there is an upper limit. With Antique 2000 I
hit it for the first time trying to base a report on a badly unnormalized
table with 89 fields!
I got a message saying that there were too many fields to create a report.
Evi