There are two different bugs in the system that can affect drilling into bar charts.
The first occurs when using two group by fields in your report. Our suggestion is to remove one of the group by clauses which will allow you to drill in seamlessly.
The second occurs when using a date field as a group by field. The issue occurs because the report charts are unable to recognise date formats other that the american YYYYMMDD.
So if you have your date format set to DDMMYYYY then the report doesn't find anything for that. The workaround is to swap your date format to be one of the YYYYMMDD iterations. To do this:
Go to the user menu
Select Profile
Choose Edit
On the Advanced tab, edit the Date Format dropdown
Press Save
Once you have done this and queried the report, you can edit the date format back using the same method.