Unable to group by date in Pivot Table

[ShawnMoon]

In the pivot table I have set up, it is organized by days, but whenever I try to group it by week, it doesn't allow me the option.

From looking up on other websites, a grouping dialogue should pop up to allow me to enter a starting and ending date, but no such dialogue occurs for me whenever I try to group. Whenever I try to right click a date, it gives me a message saying

I have tried on both Windows and Mac, but I get the same result and I cannot group my PivotTable by week.

Any help on what my problem is? Could it be the software itself?

[#2]

The inability to group on date usually suggests there's at least one text item in the dates column. It could be something as simple as a bad date or an obvious text entry. Go to the source data, drop a filter on the data, and inspect the filter. If there's an entry (or two) that doesn't consolidate with your dates, you have the answer.

[#3]

@ShawnMoon 

Are you sure that the values are real dates and not text values looking like dates?

Does the date column in the data source contain empty cells, or non-date values?