Grouping in Pivot Table
 

We have had a report operating successfully for some time as a pivot table in
Microsoft Excel (from an ODBC connection to a SQL Server database).

We have just started getting an error
"A field in your source data has more unique items than can be used in a
PivotTable. Microsoft Excel may not be able to create the PivotTable or may
create the PivotTable without the data from this field.".

So I find the relevant fields (one with 8900 distinct entries and one with
over 200,000 distinct entries) and I remove them from the report. Error
keeps occurring.

So I create a new report and drag all the fields in. No error. However as
soon as I try to group the dates (ActivityDate) by 7 days the error occurs.

So I create a pivot table with just the dates. Again no problems and there
are just over 1000 items. Then I try to group on them on 7 days. The error
occurs again.

I can group on months or years with no problems. It simply falls over with
this error as soon as I try to group by 7 days - despite only having 1000
distinct entries (with 200,000 total entries).

Any assistance appreciated.