Kim,
Are the controls on the report bound directly to the fields in the
query? Or are there calculations being done on the report itself? How
does the report "know" which figures are supposed to be for "previous
month"? Can you post back with the SQL view of the query?
If you look at the On Open event property of the report, it is possible
that there is an event procedure there which manipulates the Record
Source of the report at run time. It doesn't sound likely, but was just
a thought.
Presumably the report is being opened/previewed/printed via an event
somewhere? The Click event of a command button or something? Normally
by using an OpenReport macro or OpenReport method in VBA code? If so,
there may be a "where condition" argument in the macro or code that
applies an additional criteria to the data. Again, just a thought.