Report parameter is not populated with exact value in stacked column click throughs

Question

I have stacked column chart to show below opportunity data.
Category axis: Month of created date
Series: sales stage
Aggregate: runningvalue of revenue on sales stage group. 
data set has below fields.
1. opportunity id
2. created date
3. revenue
4. sales stage.
5. Calculated field: month of created date
I have a sub report which shows the detail information for that month when I click on Stacked column. In order to achieve this i have to pass a report parameter with month of created date(calculated field) on the click action of main report.
This report parameter is not getting populated when i click on the respective stacked column because of which the sub report is failing.
Any thoughts?
1. Category: month of the created date of opportunity(this 
1. Category: month of the created date of opportunity(this 

Answer 1

Thanks Katherine for reply. 
Creating a subreport was never an issue, the issue was when I click on the stacked column the parameter (A) as per your screenshot was not getting populated, some times it just passes a null value.
In my report below is the sample data and in Chart
1. Series Aggregate is on Runningvalue of Revenue set to stage scope.
2. CAtegory group is on Month of Created date
3. Series group is on Stage
4. Have a report filter for Year.
Sub report parameter: Month which is passed when  I click on the stacked column.
Below is sample data how my data looks like.
id
stage
createdon
revenue
1
U
1/1/2013
1000
2
Ir
1/2/2013
2000
3
Ir
2/2/2013
1000
4
A
2/3/2013
5000
5
A
3/3/2013
1000
6
Ir
3/3/2013
5000
7
Ir
4/3/2013
7000
Below is the image of actual report
In the above screenshot When i click on Region A or Region C for Aug Column, the Month Parameter for subreport is always null. When I click on Region B , parameter is having the
value as "Aug". 
Let me know is there anything I am missing.